Process for recovering and recycling an acid catalyst

ABSTRACT

Disclosed is a process for the extractive recovery of an acid catalyst from an aqueous mixture of glycolic acid with an extraction solvent comprising a tertiary amine or an onium carboxylate compound, a modifier, and a diluent. The acid catalyst, which can comprise strong acids such as sulfuric acid, alkyl sulfonic acids, and fluoroalkyl sulfonic acids, can be recovered by back extraction with aqueous formaldehyde and recycled to a process for the preparation of glycolic acid by the acid-catalyzed carbonylation of formaldehyde.

FIELD OF THE INVENTION

This invention pertains to the recovery of an acid catalyst from an aqueous glycolic acid mixture. More particularly, this invention pertains to a process for the extractive recovery of an acid catalyst from an aqueous glycolic acid mixture in the presence of a tertiary amine or an onium carboxylate compound, a modifier, and a diluent. The acid catalyst can be recycled to a process for the preparation of glycolic acid by the acid-catalyzed reaction of formaldehyde with carbon monoxide.

BACKGROUND OF THE INVENTION

Glycolic acid can be produced by the reaction of aqueous formaldehyde and carbon monoxide in the presence of an acid catalyst. This reaction is often referred to as the “hydrocarboxylation” or “carbonylation” of formaldehyde. The formaldehyde reactant is generally prepared by well-known methods as a aqueous mixture that contains about 35 to about 70 weight percent formaldehyde.

The hydrocarboxylation reaction is catalyzed by strong acids, either heterogeneous or homogeneous in nature. When using a homogeneous catalyst, as exemplified by sulfuric acid, the production of a purified glycolic acid product requires the removal of the acid catalyst from the reactor effluent. The glycolic acid product, however, is an unusually strong carboxylic acid (pKa ^(˜)3.8) and is capable of strong hydrogen-bonding and polar interactions with water. These properties make the separation and recycle of the hydrocarboxylation acid catalyst from the glycolic acid product difficult. For example, conditions that are useful for the extraction of the acid catalyst frequently will result in the coextraction of excessive amounts of glycolic acid or water with the acid catalyst. Moreover, for environmental and economic reasons, it is often desirable to isolate the strong acid catalyst in a form that permits its recycle to the hydrocarboxylation reactor.

One solution to recovering strong acid catalysts from aqueous glycolic acid reaction mixtures is to convert the acid catalyst to an easily separable or insoluble salt. For example, U.S. Pat. No. 2,153,064 discloses a process in which the crude glycolic acid effluent from a sulfuric acid-catalyzed hydrocarboxylation reaction is treated with calcium carbonate to precipitate the sulfuric acid as calcium sulfate. This inorganic salt must be separated and disposed of or sold as a low value by-product. In another example, described in U.S. Pat. No. 3,859,349, a sulfuric acid catalyst is removed the glycolic acid product mixture by absorption using a basic resin. The resin is regenerated by addition of aqueous ammonia, and the absorbed sulfuric acid is converted into ammonium sulfate, which is removed from the process. The ammonium sulfate may be sold as a fertilizer or otherwise disposed of, but is not recycled to the hydrocarboxylation reactor. Although these methods are effective for separating the acid catalysts from the glycolic acid product, they do not provide for the direct recovery and recycle of the acid catalyst to the formaldehyde hydrocarboxylation reaction. These limitations point to the need for a process in which a homogeneous acid catalyst for the hydrocarboxylation of aqueous formaldehyde with carbon monoxide can be recovered and optionally recycled in an efficient and cost-effective manner.

SUMMARY OF THE INVENTION

We have found that strong acid catalysts can be efficiently separated from aqueous mixtures of glycolic acid prepared by the hydrocarboxylation of aqueous formaldehyde solutions with carbon monoxide without extracting significant quantities of glycolic acid or other by-products. The recovered acid catalyst may be back extracted directly into aqueous formaldehyde and the resulting aqueous formaldehyde extract used as a reactant in the hydrocarboxylation reaction without further concentration. One aspect of our invention, therefore, is a process for recovering an acid catalyst from aqueous glycolic acid, comprising

-   (A) extracting an aqueous glycolic acid mixture, comprising     -   (i) about 50 to about 95 weight percent glycolic acid, based on         the total weight of the aqueous glycolic acid mixture, and     -   (ii) about 0.2 to about 12 weight percent, based on the total         weight of the aqueous glycolic acid mixture, of an acid catalyst         comprising sulfuric acid, an alkyl sulfonic acid containing from         1 to 5 carbon atoms, a fluoroalkyl sulfonic acid containing from         1 to 5 carbon atoms, or a combination thereof;     -   with an extraction solvent, comprising     -   (i) about 5 to about 45 weight percent, based on the total         weight of the extraction solvent, of at least one tertiary amine         containing from 12 to 40 carbon atoms, at least one onium         carboxylate compound, or a combination thereof;     -   (ii) about 5 to about 45 weight percent of at least one modifier         comprising an aliphatic carboxylic acid containing from 5 to 16         carbon atoms, a fluoroalkyl carboxylic acid containing 5 to 16         carbon atoms, an organophosphorus acid containing from 5 to 16         carbon atoms, or a combination thereof; and     -   (iii) about 10 to about 90 weight percent of at least one         diluent comprising carbon dioxide, an aliphatic hydrocarbon         containing from 3 to 25 carbon atoms, an aromatic hydrocarbon         containing 6 to 25 carbon atom, a halogenated hydrocarbon         containing 6 to 25 carbon atoms, or a combination thereof;     -   to form an aqueous raffinate phase comprising a major amount of         the glycolic acid contained in the aqueous glycolic acid mixture         and an organic extract phase comprising a major amount of the         acid catalyst contained in the aqueous glycolic acid mixture; -   (B) separating the aqueous raffinate and organic extract phases; and -   (C) extracting the organic extract phase from step (B) with an     aqueous formaldehyde solution to form an aqueous formaldehyde     extract comprising a major amount of the acid catalyst contained in     the organic extract phase from step (B) and an organic raffinate     phase comprising a minor amount of the acid catalyst contained in     the organic extract phase.

Typical acid catalysts that may be recovered using the process of the invention include, but are not limited to, sulfuric acid, trifluoromethanesulfonic acid, methanesulfonic acid, methanedisulfonic acid, methanetrisulfonic acid, bis(methylsulfonyl)methanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic acid, or a combination thereof. We have discovered also that a wash step can be effectively used to recover the tertiary amine and/or onium carboxylate compound and modifier from the glycolic acid raffinate to control their potential loss. Accordingly, in another embodiment of the invention, our recovery process may further comprise:

extracting the aqueous raffinate phase from step (B) with a wash solvent comprising about 80 to about 100 weight percent, based on the total weight of the wash solvent, of a wash diluent comprising carbon dioxide, an aliphatic hydrocarbon containing from 3 to 25 carbon atoms, an aromatic hydrocarbon containing 6 to 25 carbon atoms, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof; and about 0 to about 20 weight percent of a wash modifier comprising an aliphatic carboxylic acid containing from 5 to 16 carbon atoms, an organophosphorus acid containing from 5 to 16 carbon atoms, an alkanol containing 6 to 12 carbon atoms, or a combination thereof, to form a washed aqueous raffinate phase and an organic wash extract phase, wherein the weight ratio of the wash solvent to the aqueous raffinate phase is about 0.1:1 to about 1:1;

separating the washed aqueous raffinate and organic wash extract phases, and

combining the organic wash extract phase with the extraction solvent of step (A) or with the organic extract phase of step (B).

The acid catalysts that are extracted into the organic extract phase can be back extracted into aqueous formaldehyde and recycled into the hydrocarboxylation reaction. Hence, another embodiment of our invention is a process for recovering an acid catalyst from aqueous glycolic acid, comprising

-   (A) extracting an aqueous glycolic acid mixture, comprising     -   (i) about 70 to about 90 weight percent glycolic acid, based on         the total weight of the aqueous glycolic acid mixture, and     -   (ii) about 1 to about 10 weight percent of an acid catalyst         comprising sulfuric acid, methanesulfonic acid,         methanedisulfonic acid, methanedisulfonic acid,         bis(methylsulfonyl)methanesulfonic acid,         trifluoromethanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic         acid or a combination thereof;     -   with an extraction solvent, comprising     -   (i) about 5 to about 45 weight percent, based on the total         weight of the extraction solvent, a tertiary amine comprising         tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trioctylamine,         triisooctylamine, triisodecyl amine, tridodecylamine,         tridecylamine, dioctyldecylamine, didecyloctylamine, or a         combination thereof;     -   (ii) about 5 to about 45 weight percent of a modifier comprising         2-ethylhexanoic acid, lauric acid, perfluorooctanoic acid,         bis(2-ethylhexyl)hydrogen phosphate, or a combination thereof,         wherein the weight ratio of the modifier to the tertiary amine         is about 1:1 to about 5:1;     -   (iii) about 10 to about 90 weight percent of a diluent         comprising hexane, heptane, decane, methylcyclohexane, benzene,         toluene, xylene, or a combination thereof;         -   to form an aqueous raffinate phase comprising a major amount             of the glycolic acid contained in the aqueous glycolic acid             mixture and an organic extract phase comprising a major             amount of the acid catalyst contained in the aqueous             glycolic acid mixture; -   (B) separating the aqueous raffinate and organic extract phases; -   (C) extracting the organic extract phase from step (B) with an     aqueous formaldehyde solution, comprising about 35 to about 85     weight percent formaldehyde, based on the total weight of the     aqueous formaldehyde solution, to form an aqueous formaldehyde     extract comprising a major amount of the acid catalyst contained in     the organic extract phase from step (B) and an organic raffinate     phase comprising a minor amount of the acid catalyst contained in     the organic extract phase;

(D) contacting the aqueous raffinate phase from step (B) with a wash solvent comprising about 80 to about 100 weight percent, based on the total weight of the wash solvent, of a wash diluent comprising hexane, heptane, decane, methylcyclohexane, benzene, toluene, xylene, or a combination thereof; and about 0 to about 20 weight percent of a wash modifier comprising 2-ethylhexanoic acid, lauric acid, bis(2-ethylhexyl)hydrogen phosphate, 2-ethylhexanol, 2-ethylbutanol, n-hexanol, n-octanol, n-decanol, or a combination thereof, to form a washed aqueous raffinate phase and an organic wash extract phase, wherein the weight ratio of the wash solvent to the aqueous raffinate phase is about 0.1:1 to about 1:1;

-   (E) separating the washed aqueous raffinate and organic wash extract     phases; and -   (F) combining the organic wash extract phase with the extraction     solvent of step (A) or with the organic extract phase of step (B).

DETAILED DESCRIPTION

The present invention provides a means to recover and, optionally, recycle homogeneous, strong acid catalysts from aqueous glycolic acid mixtures that are prepared by the hydrocarboxylation of aqueous formaldehyde solutions. In a general embodiment, therefore, our invention provides a process for recovering an acid catalyst from aqueous glycolic acid, comprising

-   (A) extracting an aqueous glycolic acid mixture, comprising     -   (i) about 50 to about 95 weight percent glycolic acid, based on         the total weight of the aqueous glycolic acid mixture, and     -   (ii) about 0.2 to about 12 weight percent, based on the total         weight of the aqueous glycolic acid mixture, of an acid catalyst         comprising sulfuric acid, an alkyl sulfonic acid containing from         1 to 5 carbon atoms, a fluoroalkyl sulfonic acid containing from         1 to 5 carbon atoms, or a combination thereof;     -   with an extraction solvent, comprising     -   (i) about 5 to about 45 weight percent, based on the total         weight of the extraction solvent, of at least one tertiary amine         containing from 12 to 40 carbon atoms, at least one onium         carboxylate compound, or a combination thereof;     -   (ii) about 5 to about 45 weight percent of at least one modifier         comprising an aliphatic carboxylic acid containing from 5 to 16         carbon atoms, a fluoroalkyl carboxylic acid containing 5 to 16         carbon atoms, an organophosphorus acid containing from 5 to 16         carbon atoms, or a combination thereof; and     -   (iii) about 10 to about 90 weight percent of at least one         diluent comprising carbon dioxide, an aliphatic hydrocarbon         containing from 3 to 25 carbon atoms, an aromatic hydrocarbon         containing 6 to 25 carbon atom, a halogenated hydrocarbon         containing 6 to 25 carbon atoms, or a combination thereof;     -   to form an aqueous raffinate phase comprising a major amount of         the glycolic acid contained in the aqueous glycolic acid mixture         and an organic extract phase comprising a major amount of the         acid catalyst contained in the aqueous glycolic acid mixture; -   (B) separating the aqueous raffinate and organic extract phases; and -   (C) extracting the organic extract phase from step (B) with an     aqueous formaldehyde solution to form an aqueous formaldehyde     extract comprising a major amount of the acid catalyst contained in     the organic extract phase from step (B) and an organic raffinate     phase comprising a minor amount of the acid catalyst contained in     the organic extract phase.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Further, the ranges stated in this disclosure and the claims are intended to include the entire range specifically and not just the endpoint(s). For example, a range stated to be 0 to 10 is intended to disclose all whole numbers between 0 and 10 such as, for example 1, 2, 3, 4, etc., all fractional numbers between 0 and 10, for example 1.5, 2.3, 4.57, 6.1113, etc., and the endpoints 0 and 10. Also, a range associated with chemical substituent groups such as, for example, “C₁ to C₅ hydrocarbons”, is intended to specifically include and disclose C₁ and C₅ hydrocarbons as well as C₂, C₃, and C₄ hydrocarbons.

As used in the specification and the claims, the term “feed” is intended to have its commonly understood meaning in the liquid-liquid extraction art, that is the solution that contains the materials to be extracted or separated. In the present invention, one example of a “feed” is mixture of glycolic acid, water, and sulfuric acid. The term “extraction solvent,” as used herein, is intended to be synonymous with the term “extractant” and is intended to mean the immiscible liquid that is used in the extraction process to extract materials or solutes from the feed. In the present invention, one example of an extraction solvent is a solution of a tertiary amine such as tris(2-ethyl)hexylamine, a carboxylic acid modifier, such as 2-ethylhexanoic acid, and a hydrocarbon dilute, such as heptane. The term “extract” is immiscible liquid left from the extraction solvent after it has been contacted with the feed. The term “raffinate” is intended to mean the liquid phase left from the feed after it been contacted with the extraction solvent. The term “wash solvent” is understood to mean a liquid used to wash or enhance the purity of the raffinate phase. In the present invention, the wash solvent may contain one or more components such as, for example, tertiary amines, carboxylic acids, and hydrocarbon diluents.

The aqueous glycolic acid mixture may be prepared by any means known to persons skilled in the art such as, for example, by simply dissolving glycolic acid in water or by fermentation methods. Our invention is illustrated, however, with particular reference to recovering acid catalysts from aqueous glycolic acid mixtures prepared by contacting aqueous solutions of formaldehyde with carbon monoxide in the presence of an acid catalyst under elevated pressures and temperatures. These reactions are referred herein as the “hydrocarboxylation” of formaldehyde and are exemplified in U.S. Pat. Nos. 2,152,852; 2,153,064; 2,211,624; 2,211,625; and 3,948,977; and United Kingdom Patent No. 1,499,245.

The hydrocarboxylation process can be carried out by feeding carbon monoxide to a reaction mixture comprising aqueous formaldehyde in the presence of a acid catalyst. The carbon monoxide typically is supplied to the reaction mixture in sufficient excess to insure an adequate supply thereof for absorption by the formaldehyde and to retard side reactions such as, for example, the decomposition of the formaldehyde to carbon monoxide and hydrogen or other products. The amount of carbon monoxide useful for the carbonylation reaction ranges from a molar ratio of about 0.1:1 to about 1,000:1 of carbon monoxide to aldehyde, formaldehyde, or formaldehyde equivalents with a more preferred range being from about 0.5:1 to about 100:1 and a most preferred range from about 1.0:1 to about 20:1.

The composition of the carbon monoxide stream required for hydro-carboxylation may comprise carbon monoxide, hydrogen, and carbon dioxide. For example, the carbon monoxide may be supplied in substantially pure form or as a mixture with other gases such as, for example, hydrogen, carbon dioxide, methane, nitrogen, noble gases (e.g., helium and argon), and the like. For example, the carbon monoxide need not be of high purity and may contain from about 1% by volume to about 99% by volume carbon monoxide. The remainder of the gas mixture may include such gases as, for example, nitrogen, hydrogen, water, noble gases, and paraffinic hydrocarbons having from one to four carbon atoms. In order to reduce compression costs, it is desirable for the carbon monoxide stream to comprise at least 95 mole % carbon monoxide, more preferably at least 99 mole %.

The carbon monoxide may be obtained from typical sources that are well known in the art. For example, the carbon monoxide may be provided by any of a number of methods known in the art including steam or carbon dioxide reforming of carbonaceous materials such as natural gas or petroleum derivatives; partial oxidation or gasification of carbonaceous materials, such as petroleum residuum, bituminous, sub bituminous, and anthracitic coals and cokes, lignite, oil shale, oil sands, peat, biomass, petroleum refining residues or cokes, and the like. For example, the carbon monoxide may be provided to the reaction mixture as a component of synthesis gas or “syngas”, comprising carbon dioxide, carbon monoxide, and hydrogen.

The aqueous formaldehyde used in the hydrocarboxylation reaction typically comprises about 35 to about 85 weight percent formaldehyde. Other examples of formaldehyde levels in the aqueous formaldehyde feed are about 40 to about 70 weight percent and about 40 to about 60 weight percent. These ranges are typical concentrations that can be achieved with conventional formaldehyde processes without further distillation. Conventional formaldehyde processes are described in “Formaldehyde”, Kirk-Othmer Encyclopedia, Vol. 11, 4^(th) Edition, 1994. For example, commercially available formaldehyde typically contains approximately 55 weight percent formaldehyde in water. Other forms of formaldehyde may be present in the aqueous formaldehyde feedstock including trioxane or paraformaldehyde and linear polymers of formaldehyde, i.e., poly(oxymethylene)glycols and derivatives thereof, formed from the polymerization or oligomerization of formaldehyde in water or other solvents. The term “formaldehyde”, as used herein in the context of the current specification and claims, is intended to include all the various forms of formaldehyde described above.

Examples of acid catalysts that can be used to catalyze the hydrocarboxylation reaction include, but are not limited to, sulfuric acid, trifluoromethanesulfonic acid (triflic acid), methanedisulfonic acid, methanetrisulfonic acid, bis(methylsulfonyl)-methanesulfonic acid, 1,1,2,2-tetrafluoroethane sulfonic acid, and combinations thereof. The acids used to catalyze the hydrocarboxylation reaction and subsequently recovered by the process of the invention may be characterized as “strong” acids; that is, acids having a pKa value in water of 1 or less. For multiprotic acids, the above definition refers to the 1^(st) pKa value. The concentration of the strong acid catalyst species in the polar reaction product fluid may vary substantially depending on the specific strong acid catalyst species used, but typically the composition ranges from about 0.5 weight percent to about 12 weight percent. In one embodiment, for example, the acid catalyst comprises sulfuric acid at a concentration range in the hydrocarboxylation reaction mixture of about 1 to about 10 weight percent or, in another example, about 1 to about 8 weight percent, based on the total weight of the reaction mixture. In the another example, the acid catalyst comprises triflic acid having concentration of about 0.2 to about 5 weight percent or, in another example, about 0.5 to about 4 weight percent, based on the total weight of the hydrocarboxylation reaction mixture. In yet another example, the acid catalyst can comprise methanetrisulfonic acid in a concentration of about 0.5 and 10 weight percent or, in another example, about 1.0 and 8 weight percent.

The hydrocarboxylation process can be conducted under continuous, semi-continuous, and batch modes of operation and may utilize a variety of reactor types. Examples of suitable reactor types include, but are not limited to, stirred tank, continuous stirred tank, trickle bed, tower, slurry, and tubular reactors. A typical temperature range for the hydrocarboxylation reaction is about 160 to about 220° C. In another example, the temperature range can be about 190 to about 210° C. Examples of pressure ranges for the hydrocarboxylation reaction about 35 to about 350 bar gauge and about 60 to about 200 bar gauge.

The reactants and acid catalyst(s) may be introduced separately or in any sequence or combination to the reactor. In addition, one or more reactants may be introduced at different locations in the reaction zone. For example, in a continuously operated process containing a catalyst bed, the addition of water or formaldehyde may be staged throughout the reaction zone. In some cases, it may be desirable to recirculate a portion of the reaction media to the reactor to act as a liquid reaction media for the next synthesis. In order to reduce by-product formation, it is desirable to set the residence time in the hydrocarboxylation reaction to give an outlet formaldehyde concentration of about 5 weight percent or less. In addition to glycolic acid, the hydrocarboxylation process typically produces glycolic acid oligomers, water, unreacted formaldehyde, unwanted polar by-products; color bodies and corrosion metals also may be present. The polar by-products may include, but are not limited to, diglycolic acid, methoxyacetic acid, methyl methoxyacetate, and formic acid. The corrosion metals will depend on the metallurgy used for the reactor and piping and can include iron, chromium, nickel, zirconium, and combinations thereof.

For the present invention, the aqueous glycolic acid mixture comprises about 50 to about 95 weight percent glycolic acid, based on the total weight the reaction mixture. Additional examples of the concentration of glycolic acid in the aqueous mixture are about 60 to about 90 weight percent and about 65 to about 90 weight percent. For example, in one embodiment, the aqueous glycolic acid mixture comprises about 70 to about 90 weight percent glycolic acid and is produced by contacting aqueous formaldehyde with carbon monoxide in the presence of an acid catalyst as described hereinabove.

The aqueous glycolic acid mixture also comprises about 0.2 to about 12 weight percent, based on the total weight of the aqueous glycolic acid mixture, of an catalyst comprising sulfuric acid, an alkyl sulfonic acid containing from 1 to 5 carbon atoms, a fluoroalkyl sulfonic acid containing from 1 to 5 carbon atoms, or a combination thereof. Some additional examples of concentrations of the acid catalyst in the aqueous glycolic acid mixture are about 0.5 to about 10 weight percent and about 1 to about 10 weight percent. For example, the acid catalyst can comprise sulfuric acid, trifluoromethanesulfonic acid, methanesulfonic acid, methanedisulfonic acid, methanetrisulfonic acid, bis(methylsulfonyl)methanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic acid, or a combination thereof. The aqueous glycolic acid solution can comprise any one of the above acids or mixtures thereof in any combination.

The aqueous glycolic acid is contacted with an extraction solvent comprising at least one tertiary amine, at least one onium carboxylate compound, or a combination thereof, and at least one diluent and at least one modifier. For example, the extraction solvent can comprise about 5 to about 45 weight percent of at least one tertiary amine containing from 12 to 40 carbon atoms, at least one onium carboxylate compound, or a combination thereof. In one embodiment, for example, the extraction solvent can comprise about 10 to about 25 weight percent of at least one tertiary amine. Some other examples of tertiary amine and/or onium carboxylate concentrations in the extraction solvent are about 5 to about 40 weight percent and about 10 to 35 weight percent. The term “tertiary amine,” as used herein, is understood to mean an amine in which three carbon atoms are attached to the amino nitrogen. Typically, the tertiary amines of the invention will comprise carbon chain units that have a sufficient number of carbon atoms to facilitate their solubility in the non-polar extract phase. The carbon chain units may be linear, branched, cyclic, or a combination thereof. For example, the carbon chain units for the tertiary amines can comprise linear or branch structures, and can have in total from 12 to 40 carbon atoms. In one example, the tertiary amine can be hindered, that is, at least one of the carbon chains contains at least one branching point at the carbon at the β position from the nitrogen atom. Some representative tertiary amines include, but are not limited to, tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trioctylamine, triisooctylamine, triisodecyl amine, tridodecylamine, tridecylamine, dioctyldecylamine, didecyloctylamine, or a combination thereof. In one embodiment, for example, the extraction solvent can comprise tris(2-ethylhexyl)amine.

The extraction solvent also can comprise about 5 to about 45 weight percent of at least one onium carboxylate compound that comprises a cation selected from quaternary atoms or radicals such as tertiary or quaternary ammonium, quaternary phosphonium, and trialkyl sulfonium. As noted above, additional examples of the concention of the onium carboxylate compound in the extraction solvent are about 5 to about 40 weight percent, about 10 to about 35 weight percent, and about 10 to about 25 weight percent. The extractant may contain the onium carboxylate compound by itself or in combination with a tertiary amine as described above. The onium carboxylate compound may include the protonated forms of the above atoms or radicals and, especially, the protonated forms of various tertiary amines. Persons of skill in the art will understand that mixtures of tertiary amines and carboxylic acids will produce some quantity of onium carboxylate compounds that result from protonation of the tertiary amines by the carboxylic acid modifier and that exist in chemical equilibrium with the free amines and carboxylic acids. Therefore, in the context of the presence invention, it will be understood also by persons skilled in the art that the presence of an onium carboxylate compound in the extraction solvent that results from the protonation of a tertiary amine and a carboxylic acid is equivalent to the addition of the tertiary amine and carboxylic acid modifier separately to the extraction process. Thus, the tertiary amine and modifier can be added to the extraction process separately, as the corresponding onium carboxylate compound, or as a combination of the tertiary amine, modifier, and onium carboxylate compound.

The onium carboxylate compound may contain any number of carbon atoms, e.g., up to 60 carbon atoms, and also may contain one or more heteroatoms. The tri- and tetraalkyl quaternary ammonium and phosphonium salts typically contain a total of 5 to 40 carbon atoms. In one embodiment, for example, the onium carboxylate compound can comprise an onium cation selected from the group consisting of R¹R²R³R⁴N⁺, R¹R²R³R⁴P⁺, R¹R²R³R⁴As⁺, and R¹R²R³S⁺, and a carboxylate anion of the type R⁵CO₂ ⁻, wherein R¹, R², R³, R⁴, and R⁵ are independently selected from alkyl or substituted alkyl moieties having up to 20 carbon atoms, cycloalkyl or substituted cycloalkyl having 5 to 20 carbon atoms, or aryl or substituted aryl having 6 to 20 carbon atoms.

Some representative examples of ammonium cations include, but are not limited to, tetrapentylammonium, tetrahexylammonium, tetraoctylammonium, tetradecylammonium, tetradodecylammonium, tetrapropylammonium, tetrabutylammonium, methyltrioctylammonium, methyltributylammonium, N-octyl-quinuclidinium, N,N′-dimethyl-N,N′-dihexadecylpiperazinium diiodide, dimethyl-hexadecyl-[3-pyrrolidinylpropyl]ammonium, N,N,N,N′,N′,N′-hexa(dodecyl)octane-1,8-diammonium, and N,N,N,N′,N′,N′-hexa(dodecyl)butane-1,4-diammonium.

Exemplary phosphonium cations include tetraoctylphosphonium, tetrabutylphosphonium, triphenyl(hexyl)phosphonium, triphenyl(octyl)phosphonium, tribenzyl(octyl)phosphonium, tribenzyl(dodecyl)phosphonium, triphenyl-(decyl)phosphonium, triphenyl(dodecyl)phosphonium, tetrakis(2-methylpropyl)phosphonium, tris(2-methylpropyl)(butyl)phosphonium, triphenyl(3,3-dimethylbutyl)-phosphonium, triphenyl(3-methylbutyl)phosphonium, tris(2-methylbutyl)(3-methyl-butyl)phosphonium, triphenyl[2-trimethylsilylethyl]phosphonium, tris(p-chlorophenyl)-(dodecyl)phosphonium, hexyltris(2,4,6-trimethylphenyl)phosphonium, tetradecyltris(2,4,6-trimethylphenyl)phosphonium, dodecyltris(2,4,6-trimethyl-phenyl)phosphonium, methyltriocytlphosphonium, tetraalkylphosphonium, methyltributylphosphonium, methyltricyclohexylphosphonium, and the like. Preferred phosphoniums include methyltriphenylphosphonium, methyltributylphosphonium, methyltriocytlphosphonium, and butyltridodecylphosphonium.

Some representative carboxylate groups include, but are not limited to, 2-ethylhexylhexanoate, n-pentanoate, 2-methylbutanoate, 3-methylbutanoate, hexanoate, 2-ethylbutanoate, heptanoate, octanoate, pelargonoate, nonanoate, decanoate, laurate, palmitate, perfluorooctanoate, or a combination thereof. In addition to the onium carboxylate compounds described above, the onium carboxylate compound may also include ammonium carboxylates salts formed from one or more of the tertiary amines and one or more aliphatic carboxylic acids described herein. For example, the onium carboxylate salt can comprise tris(2-ethylhexyl)ammonium 2-ethylhexanoate, formed from the reaction of tris(2-ethylhexyl)amine and 2-ethylhexanoic acid. In another embodiment of the invention, the acid catalyst can be triflic acid and the extraction solvent can comprise an onium carboxylate compound that comprises hydrogen tris(2-ethylhexyl)ammonium perfluorooctanoate. This latter onium carboxylate compound can be formed outside of the extraction process and added directly to the extraction solvent or formed in situ by adding tris(2-ethylhexyl)amine and perfluorooctanoic acid to the extraction solvent mixture.

In addition to at least one tertiary amine and/or onium carboxylate compound, the extraction solvent can comprise about 5 to about 45 weight percent of at least one modifier, comprising an aliphatic carboxylic acid containing from 5 to 16 carbon atoms, a fluoroalkyl carboxylic acid containing 5 to 16 carbon atoms, an organophosphorus acid containing from 5 to 16 carbon atoms, or a combination thereof. In one embodiment, the modifier does not react readily under either hydrocarboxylation or hydrogenation reaction conditions.

Some specific examples of modifiers include n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, bis(2-ethylhexyl)hydrogen phosphate, perfluorooctanoic acid, or a combination thereof. For example, in one embodiment of our process, the acid catalyst comprises trifluoromethanesulfonic acid; the tertiary amine comprises tris(2-ethylhexyl)amine; and the modifier comprises perfluorooctanoic acid. Typically, the weight ratio of the modifier to the tertiary amine, onium carboxylate compound, or the combination of the tertiary amine and the onium carboxylate compound will be in the range of about 0.1:1 to about 5:1. Some other examples of weight ratio of modifier to tertiary amine, onium carboxylate compound, or the combination thereof are about 0.5:1 to about 5:1, about 1:1 to about 5:1, and about 2:1 to about 5:1. In embodiments where the extractant comprises an onium carboxylate compound that results from the protonation of a tertiary amine with the carboxylic acid modifier, the ratio of modifier to tertiary amine may be determined from the total equivalents of tertiary amine and carboxylic acid. For example, the ratio may be determined from the weight ratio of the free tertiary amine and carboxylic acid present in extraction solvent and the weight equivalents of tertiary amine and carboxylic acid present as in form of the onium carboxylate compound.

The extraction solvent further comprises about 10 to about 90 weight percent, based on the total weight of the extraction solvent, of at least one diluent to help form an immiscible liquid phase with the aqueous glycolic acid mixture and to impart physical and transport properties that facilitate the separation of the strong acid catalyst from the glycolic acid. For example, the diluent concentration in the extraction solvent can be about 20 to about 80 weight percent. Typically, the extraction solvent can have a difference in specific gravity of at least 0.05 grams/mL with respect to the aqueous glycolic acid mixture. For example, the density of an aqueous glycolic acid mixtures, comprising typically about 70 to about 90 weight percent aqueous glycolic acid and about 1 to about 10 weight percent acid catalyst is typically in the range of about 1.1 to about 1.45 grams/mL at 40° C. In this example, the density of the extraction solvent can differ by at least 0.05 grams/mL from this range, that is density of the diluent can be less than about 1.05 g/mL or greater than about 1.50 g/mL. In another embodiment, the density of the diluent is lower than the density of the aqueous glycolic acid solution by at least 0.10 g/mL. In yet another embodiment, the density difference between the aqueous glycolic acid mixture and the diluent can be less than 0.05 grams/mL, but this may require the use of a centrifugal extractor, which can increase the cost of the process.

The diluent typically will have a low viscosity of about 10 centipoise at the extraction temperature. Some general classes of compounds that can be used as diluents in the process of the invention include carbon dioxide, aliphatic hydrocarbon containing from 3 to 25 carbon atoms, aromatic hydrocarbon containing 6 to 25 carbon atom, halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof. For example, the diluent can be an aliphatic or aromatic hydrocarbon containing about 6 to about 16 carbon atoms. Mixtures of hydrocarbons may be used. Some specific, additional examples of diluents include pentane, hexane, heptane, decane, methylcyclohexane, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, benzene, toluene, xylene, or a combination thereof. For example, the diluent may comprise isoparaffinic mixed hydrocarbons having boiling ranges between about 90 and about 325° C., as exemplified by the ISOPAR™ solvents, such as ISOPAR C (boiling point range of 98 to 104° C.), Isopar E (boiling point range of 118 to 137° C.), ISOPAR G (boiling point range of 160 to 176° C.), ISOPAR H (boiling point range of 178 to 188° C.), ISOPAR K (boiling point range of 178 to 197° C.), ISOPAR L (boiling point range of 189 to 207° C.), ISOPAR C (boiling point range of 223 to 254° C.), and ISOPAR V (boiling point range of 273 to 312° C.).

Dense gases and supercritical fluids, for example, carbon dioxide and propane, also may be used as the diluent, either alone or in combination with other diluents. In one example of the instant invention, the acid catalyst comprises sulfuric acid; the tertiary amine comprises tris(2-ethylhexyl)amine; the modifier comprises 2-ethylhexanoic acid, and the diluent comprises hexane, heptane, decane, or a combination thereof.

The extraction of the aqueous glycolic acid mixture can be carried out by any means known in the art to intimately contact two immiscible liquid phases and to separate the resulting phases after the extraction procedure. For example, the extraction can be carried out using columns, centrifuges, mixer-settlers, and miscellaneous devices. Some representative examples of extractors include unagitated columns (e.g., spray, baffle tray and packed, perforated plate), agitated columns (e.g., pulsed, rotary agitated, and reciprocating plate), mixer-settlers (e.g., pump-settler, static mixer-settler, and agitated mixer-settler), centrifugal, and other miscellaneous extractors (e.g., emulsion phase contactor, electrically enhanced extractors, and membrane extractors). A description of these devices can be found in the Handbook of Solvent Extraction, Krieger Publishing Company, Malabar, Fla., 1991, pp. 275-501. The various types of extractors may be used alone or in any combination.

The extraction may be conducted in one or more stages. The number of extraction stages can be selected by the best compromise between capital costs, achieving high extraction efficiency, ease of operability, and the stability of the starting materials and reaction product to the extraction conditions. The extraction also can be conducted in a batch or continuous fashion. In a continuous mode, the extraction may be carried out in a co-current, a counter-current manner, or as a fractional extraction in which multiple solvents and/or more than one solvent feed point is used to help facilitate the separation.

The aqueous glycolic acid mixture and extraction solvent can be contacted by fractional extraction methods. In this embodiment, an optional, additional polar solvent that is miscible with the aqueous glycolic acid mixture can be added to the extractor if necessary to reduce the amount of glycolic acid exiting with the organic extract phase. Some examples of polar solvents include, but are not limited to, water, ethylene glycol, glycolic acid, other liquids present in the aqueous glycolic mixture, or a combination thereof.

The extraction typically can be carried out at a temperature of about 20 to about 120° C. For example, the extraction can be conducted at a temperature of about 40 to about 85° C. The desired temperature range may be constrained further by the boiling point of the diluent component of the solvent mixture. Generally, it is undesirable to operate the extraction under conditions in which the diluent boils. The extractor for the instant invention may be operated in such a way as to establish a temperature gradient across the extractor in order to improve the mass transfer kinetics or decantation rates.

The extraction of the aqueous glycolic acid mixture produces an aqueous raffinate phase comprising a major amount of the glycolic acid contained in the aqueous glycolic acid mixture and an organic extract phase comprising a major amount of the acid catalyst contained in the aqueous glycolic acid mixture. The aqueous raffinate phase and the organic extract phase may be separated by any phase separation technology known in the art. The phase separation techniques can be accomplished in the extractor or in a separate liquid-liquid separation device. Suitable liquid-liquid separation devices include, but are not limited to, coalescers, cyclones and centrifuges. Typical equipment that can be used for liquid-liquid phase separation devices are described in the Handbook of Separation process Technology, ISBN 0-471-89558-X, John Wiley & Sons, Inc., 1987.

The acid catalyst can be back-extracted from the organic extract phase into an aqueous formaldehyde solution that subsequently can be used directly as a reactant in the hydrocarboxylation reaction. Thus, our process also comprises extracting the organic extract phase from step (B) with an aqueous formaldehyde solution to form an aqueous formaldehyde extract comprising a major amount of the acid catalyst contained in the organic extract phase from step (B) and an organic raffinate phase comprising a minor amount of the acid catalyst contained in the organic extract phase. The aqueous formaldehyde extract can be passed to a process for the preparation of glycolic acid by carbonylation of formaldehyde in the presence of an acid catalyst. Typically, the acid catalyst may be recovered at about 0.5 to about 10 weight percent in the aqueous formaldehyde extract, based on the total weight of the aqueous formaldehyde extract, and recycled to the hydrocarboxylation reaction without further concentration of the acid catalyst. The formaldehyde concentration in the aqueous formaldehyde solution generally can be about 35 to about 85 weight percent, based on the total weight of the aqueous formaldehyde solution. For example, the formaldehyde concentration can be about 40 to about 55 weight percent. This latter concentration can be obtained from conventional formaldehyde processes without further distillation. Additionally, water may be added in the aqueous formaldehyde extraction solvent if desired.

The weight ratio of the aqueous formaldehyde solution to the organic extract phase from step (B) of our inventive process about 0.05:1 to about 2:1. Further examples of weight ratios of the aqueous formaldehyde solution to the organic extract phase are about 0.1:1 to 2:1 and about 0.1:1 to about 1:1. The extraction of the acid catalyst into the aqueous formaldehyde solution can be conducted at a temperature of about 20 to about 95° C. For example, in one embodiment of the invention, steps (A)-(C) of the invention are carried out at a temperature of about 40 to about 85° C. The temperature range for step (C) of the process may be constrained by the temperature at which formaldehyde begins to fall out of solution. This constraint is a function of formaldehyde concentration and is well known in the art. A description of the temperature dependency of formaldehyde solubility as a function of temperature can be found in Walker, Formaldehyde, Walker, ACS Monograph, Washington, D.C., ACS, 1964, p. 95. Generally, the temperature for the back extraction of the acid catalyst into the aqueous formaldehyde solution can be about 2 to about 10° C. higher than the temperature at which formaldehyde begins to fall out of solution for the chosen concentration of the aqueous formaldehyde solution. The back extraction for the instant invention may be operated in such a way as to establish a temperature gradient across the extraction vessel.

The efficacy of back extraction may be enhanced by modification of the composition of the organic extract phase from step (A) of the instant process by adding an optional non-polar additive that comprises one or more non-polar compounds or mixture of compounds. The non-polar additive can comprise the same compound or mixture of compounds used as the diluent or modifier in step (A) of the process. For example, the non-polar additive can comprise a composition which is readily recoverable by distillation of the organic raffinate phase from the back extraction step. The resulting organic raffinate phase, with or without distillation, can be recycled to the extraction in step (A) for reuse in the extraction of the aqueous glycolic acid mixture. The aqueous formaldehyde solution and the organic extract also can be contacted by fractional extraction methods. In this embodiment, a non-polar additive as described above that is miscible with the organic raffinate phase can be added to the extractor if necessary to reduce the amount of organic extract phase components (other than the acid catalyst) exiting with the aqueous formaldehyde extract.

Depending on the tertiary amine and modifier, it may be desirable to wash the aqueous raffinate in step (B) to recover any tertiary amine, onium carboxylate compound, diluent, and modifier from the aqueous raffinate phase. Our process, therefore, further comprises extracting the aqueous raffinate phase from step (B) with a wash solvent comprising about 80 to about 100 weight percent, based on the total weight of the wash solvent, of a wash diluent comprising carbon dioxide, an aliphatic hydrocarbon containing from 3 to 25 carbon atoms, an aromatic hydrocarbon containing 6 to 25 carbon atoms, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof; and about 0 to about 20 weight percent of a wash modifier comprising an aliphatic carboxylic acid containing from 5 to 16 carbon atoms, an organophosphorus acid containing from 5 to 16 carbon atoms, an alkanol containing 6 to 12 carbon atoms, or a combination thereof, to form a washed aqueous raffinate phase and a organic wash extract phase, separating the washed aqueous raffinate and organic wash extract phases, and combining the organic wash extract phase with the extraction solvent of step (A) or with the organic extract phase of step (B).

The above wash step may be accomplished by any means known in the art such as, for example, by extracting the aqueous raffinate phase with the wash solvent in any of the various extraction centrifuges, mixer-settlers, and other extraction devices described hereinabove. The weight ratio of wash solvent to aqueous raffinate phase can be about 0.1:1 to about 1:1. An additional example of this weight ratio is about 0.2:1 to about 0.5:1. The wash step can be conducted at a temperature of about 20 to 120° C. or, in another example, at about 40 to about 85° C. As noted for the other extraction steps in present invention, the temperature range of the wash step may be limited by the boiling point of the wash solvent. Also, the wash step can be operated in such a way as to establish a temperature gradient across the wash vessel.

The wash solvent typically will comprise some or all of the same components as set forth for the extraction solvent in step (A). For example, the wash solvent can comprise about 80 to about 100 weight percent of a wash diluent that comprises carbon dioxide, an aliphatic hydrocarbons containing from 3 to 25 carbon atoms, an aromatic hydrocarbon containing 6 to 25 carbon atoms, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof. Some representative examples of wash solvents include propane, butane, hexane, heptane, decane, methylcyclohexane, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, benzene, toluene, xylene, or a combination thereof. For example, the wash solvent may comprise isoparaffinic mixed hydrocarbons having boiling ranges between about 90 and about 325° C. as described previously.

The wash solvent also can comprise 0 to about 20 weight percent, based on the total weight of the wash solvent of a wash modifier. The wash modifier, typically, is a polar compound added to the wash solvent that can improve wash efficiency, i.e., the extraction of the tertiary amine, modifier, and diluent into the wash solvent. Suitable wash modifiers include carboxylic acids having from 5 to 16 carbon atoms, organo-phosphorus acids, alkanols having from 5 to 12 carbon atoms, or a combination thereof. Some specific examples of preferred wash modifiers include, but are not limited to n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, perfluorooctanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, bis(2-ethylhexyl)hydrogen phosphate, n-hexanol, 2-ethylhexanol, 2-ethylbutanol, n-octanol, isooctanol, n-decanol, isodecanol, or a combination thereof. In one embodiment, for example, the wash solvent can comprise a composition which is readily recoverable by distillation of the organic wash extract phase from the wash step.

The wash step of this invention may be conducted in one or more extraction stages. The exact number of extraction stages will be governed by the best compromise between the capital costs of having more stages and the operating costs associated with using larger amounts of the wash solvent in order to achieve the desired extraction efficiency. The wash step may be conducted in either batch or continuous mode. When conducted continuously, the wash step may be conducted in a co-current or counter-current manner. The non-polar wash phase exiting the wash step can be fed to the primary extractor. The wash step may be performed in one or more extractors that are physically separated from the extraction of step (A) or, in another embodiment, the extraction of step (A) and the wash step can occur in the same countercurrent extractor. The wash step can be conducted in one or more of the various extractors described hereinabove for steps (A)-(C) of the instant invention.

The washed aqueous raffinate phase and the organic wash extract phase are separated and the organic wash extract may be combined with the extraction solvent of step (A) or with the organic extract phase of step (B). The washed aqueous raffinate and the organic wash extract phases can be separated by any phase separation technology known in the art and described previously herein.

Another aspect of our invention is a process for recovering an acid catalyst from aqueous glycolic acid, comprising

-   (A) extracting an aqueous glycolic acid mixture, comprising     -   (i) about 70 to about 90 weight percent glycolic acid, based on         the total weight of the aqueous glycolic acid mixture, and     -   (ii) about 1 to about 10 weight percent, based on the total         weight of the aqueous glycolic acid mixture, of an acid catalyst         comprising sulfuric acid, methanesulfonic acid,         methanedisulfonic acid, methanedisulfonic acid,         bis(methylsulfonyl)methanesulfonic acid,         trifluoromethanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic         acid, or a combination thereof;     -   with an extraction solvent, comprising     -   (i) about 5 to about 45 weight percent, based on the total         weight of the extraction solvent, a tertiary amine comprising         tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trioctylamine,         triisooctylamine, triisodecyl amine, tridodecylamine,         tridecylamine, dioctyldecylamine, didecyloctylamine, or a         combination thereof;     -   (ii) about 5 to about 45 weight percent of a modifier comprising         2-ethylhexanoic acid, lauric acid, perfluorooctanoic acid,         bis(2-ethylhexyl)hydrogen phosphate, or a combination thereof,         wherein the weight ratio of the modifier to the tertiary amine         is about 1:1 to about 5:1; and     -   (iii) about 10 to about 90 weight percent of a diluent         comprising hexane, heptane, decane, methylcyclohexane, benzene,         toluene, xylene, or a combination thereof;     -   to form an aqueous raffinate phase comprising a major amount of         the glycolic acid contained in the aqueous glycolic acid mixture         and an organic extract phase comprising a major amount of the         acid catalyst contained in the aqueous glycolic acid mixture; -   (B) separating the aqueous raffinate and organic extract phases; and -   (C) extracting the organic extract phase from step (B) with an     aqueous formaldehyde solution, comprising about 35 to about 85     weight percent formaldehyde, based on the total weight of the     aqueous formaldehyde solution, to form an aqueous formaldehyde     extract comprising a major amount of the acid catalyst contained in     the organic extract phase from step (B) and an organic raffinate     phase comprising a minor amount of the acid catalyst contained in     the organic extract phase; -   (D) contacting the aqueous raffinate phase from step (B) with a wash     solvent comprising about 80 to about 100 weight percent, based on     the total weight of the wash solvent, of a wash diluent comprising     hexane, heptane, decane, methylcyclohexane, benzene, toluene,     xylene, or a combination thereof; and about 0 to about 20 weight     percent of a wash modifier comprising 2-ethylhexanoic acid, lauric     acid, bis(2-ethylhexyl)hydrogen phosphate, 2-ethylhexanol,     2-ethylbutanol, n-hexanol, n-octanol, n-decanol, or a combination     thereof, to form a washed aqueous raffinate phase and an organic     wash extract phase, wherein the weight ratio of the wash solvent to     the aqueous raffinate phase is about 0.1:1 to about 1:1; -   (E) separating the washed aqueous raffinate and organic wash extract     phases; and -   (F) combining the organic wash extract phase with the extraction     solvent of step (A) or with the organic extract phase of step (B).     It is understood that the above process comprises the various     embodiments of the aqueous glycolic acid mixture, the acid catalyst,     the tertiary amine, the modifier, diluent, and washing steps as     described previously. For example, the aqueous glycolic acid mixture     can be prepared by a process comprising the carbonylation of     formaldehyde in the presence of a sulfuric acid catalyst. In another     example, the aqueous formaldehyde solution of step (C) can comprise     about 40 to about 55 weight percent formaldehyde and the aqueous     formaldehyde extract of step (C) is passed to the glycolic acid     process. In a further example, the catalyst can comprise sulfuric     acid; the tertiary amine can comprise tris(2-ethylhexyl)amine; the     modifier can comprise 2-ethylhexanoic acid; the diluent can comprise     hexane, heptane, decane, or a combination thereof; the wash solvent     can comprise hexane, heptane, decane, or a combination thereof; the     wash modifier can comprise 2-ethylhexanoic acid, n-hexanol,     n-decanol, or a combination thereof; and the weight ratio of the     modifier to the tertiary amine is about 2:1 to about 4:1. The     aqueous formaldehyde extract can comprise about 0.5 to about 10     weight percent sulfuric acid, based on the total weight of the     aqueous formaldehyde extract.

The invention also includes the following embodiments that are set forth below and in paragraphs [0048]-[0061]: a process for recovering an acid catalyst from aqueous glycolic acid, comprising

-   (A) extracting an aqueous glycolic acid mixture, comprising     -   (i) about 50 to about 95 weight percent glycolic acid, based on         the total weight of the aqueous glycolic acid mixture, and     -   (ii) about 0.2 to about 12 weight percent, based on the total         weight of the aqueous glycolic acid mixture, of an acid catalyst         comprising sulfuric acid, an alkyl sulfonic acid containing from         1 to 5 carbon atoms, a fluoroalkyl sulfonic acid containing from         1 to 5 carbon atoms, or a combination thereof;     -   with an extraction solvent, comprising     -   (i) about 5 to about 45 weight percent, based on the total         weight of the extraction solvent, of at least one tertiary amine         containing from 12 to 40 carbon atoms, at least one onium         carboxylate compound, or a combination thereof;     -   (ii) about 5 to about 45 weight percent of at least one modifier         comprising an aliphatic carboxylic acid containing from 5 to 16         carbon atoms, a fluoroalkyl carboxylic acid containing 5 to 16         carbon atoms, an organophosphorus acid containing from 5 to 16         carbon atoms, or a combination thereof; and     -   (iii) about 10 to about 90 weight percent of at least one         diluent comprising carbon dioxide, an aliphatic hydrocarbon         containing from 3 to 25 carbon atoms, an aromatic hydrocarbon         containing 6 to 25 carbon atom, a halogenated hydrocarbon         containing 6 to 25 carbon atoms, or a combination thereof;     -   to form an aqueous raffinate phase comprising a major amount of         the glycolic acid contained in the aqueous glycolic acid mixture         and an organic extract phase comprising a major amount of the         acid catalyst contained in the aqueous glycolic acid mixture; -   (B) separating the aqueous raffinate and organic extract phases; and -   (C) extracting the organic extract phase from step (B) with an     aqueous formaldehyde solution to form an aqueous formaldehyde     extract comprising a major amount of the acid catalyst contained in     the organic extract phase from step (B) and an organic raffinate     phase comprising a minor amount of the acid catalyst contained in     the organic extract phase.

A process that includes the embodiments of paragraph [0047] in which the aqueous glycolic acid mixture comprises about 70 to about 90 weight percent glycolic acid and is produced by contacting aqueous formaldehyde with carbon monoxide in the presence of an acid catalyst.

A process that includes the embodiments of any one of paragraphs [0047]-[0048] in which the acid catalyst comprises sulfuric acid, trifluoromethanesulfonic acid, methanesulfonic acid, methanedisulfonic acid, methanetrisulfonic acid, bis(methylsulfonyl)methanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic acid, or a combination thereof.

A process that includes the embodiments of any one of paragraphs [0047]-[0049], wherein the tertiary amine comprises tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trioctylamine, triisooctylamine, triisodecyl amine, tridodecylamine, tridecylamine, dioctyldecylamine, didecyloctylamine, or a combination thereof.

A process that includes the embodiments of any one of paragraphs [0047]-[0050], in which the modifier comprises n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, bis(2-ethylhexyl)hydrogen phosphate, perfluorooctanoic acid, or a combination thereof.

A process that includes the embodiments of any one of paragraphs [0047]-[0051], in which the diluent comprises pentane, hexane, heptane, decane, methylcyclohexane, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, benzene, toluene, xylene, or a combination thereof.

A process that includes the embodiments of any one of paragraphs [0047]-[0052], in which the aqueous formaldehyde solution comprises about 35 to about 85 weight percent formaldehyde, the aqueous formaldehyde extract comprises about 0.5 to about 10 weight percent, based on the total weight of the aqueous formaldehyde extract, of the acid catalyst, and the weight ratio of the aqueous formaldehyde solution to the organic extract phase is about 0.1:1 to about 1:1.

A process that includes the embodiments of any one of paragraphs [0047]-[0053], in which the acid catalyst comprises trifluoromethanesulfonic acid; the tertiary amine comprises tris(2-ethylhexyl)amine; and the modifier comprises perfluorooctanoic acid.

A process that includes the embodiments of any one of paragraphs [0047]-[0053], in which the acid catalyst comprises sulfuric acid; the tertiary amine comprises tris(2-ethylhexyl)amine; the modifier comprises 2-ethylhexanoic acid, and the diluent comprises hexane, heptane, decane, or a combination thereof.

A process that includes the embodiments of any one of paragraphs [0047]-[0055], wherein steps (A) and (C) are carried out at a temperature of about 40 to about 85° C.

A process that includes the embodiments of any one of paragraphs [0047]-[0056], in which the aqueous formaldehyde extract is passed to a process for the preparation of glycolic acid by the carbonylation of formaldehyde in the presence of an acid catalyst.

A process that includes the embodiments of any one of paragraphs [0047]-[0057], that further comprises

extracting the aqueous raffinate phase from step (B) with a wash solvent comprising about 80 to about 100 weight percent, based on the total weight of the wash solvent, of a wash diluent comprising carbon dioxide, an aliphatic hydrocarbon containing from 3 to 25 carbon atoms, an aromatic hydrocarbon containing 6 to 25 carbon atoms, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof; and about 0 to about 20 weight percent of a wash modifier comprising an aliphatic carboxylic acid containing from 5 to 16 carbon atoms, an organophosphorus acid containing from 5 to 16 carbon atoms, an alkanol containing 6 to 12 carbon atoms, or a combination thereof, to form a washed aqueous raffinate phase and an organic wash extract phase, wherein the weight ratio of the wash solvent to the aqueous raffinate phase is about 0.1:1 to about 1:1;

separating the washed aqueous raffinate and organic wash extract phases, and

combining the organic wash extract phase with the extraction solvent of step (A) or with the organic extract phase of step (B).

A process that includes the embodiments of paragraph [0058], in which the wash solvent comprises propane, butane, hexane, heptane, decane, methylcyclohexane, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, benzene, toluene, xylene, or a combination thereof; and the wash modifier comprises n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, perfluorooctanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, bis(2-ethylhexyl)hydrogen phosphate, n-hexanol, 2-ethylhexanol, 2-ethylbutanol, n-octanol, isooctanol, n-decanol, isodecanol, or a combination thereof.

A process that includes the embodiments of paragraph [0047] in which: the aqueous glycolic acid mixture, comprises

-   (i) about 70 to about 90 weight percent glycolic acid, based on the     total weight of the aqueous glycolic acid mixture, and -   (ii) about 1 to about 10 weight percent of an acid catalyst     comprising sulfuric acid, methanesulfonic acid, methanedisulfonic     acid, methanedisulfonic acid, bis(methylsulfonyl)methanesulfonic     acid, trifluoromethanesulfonic acid,     1,1,2,2-tetrafluoroethanesulfonic acid, or a combination thereof;     the extraction solvent, comprises -   (i) a tertiary amine comprising tris(2-ethylhexyl)amine,     tris(2-ethylbutyl)amine, trioctylamine, triisooctylamine,     triisodecyl amine, tridodecylamine, tridecylamine,     dioctyldecylamine, didecyloctylamine, or a combination thereof; -   (ii) a modifier comprising 2-ethylhexanoic acid, lauric acid,     perfluorooctanoic acid, bis(2-ethylhexyl)hydrogen phosphate, or a     combination thereof; and -   (iii) a diluent comprising hexane, heptane, decane,     methylcyclohexane, benzene, toluene, xylene, or a combination     thereof; in which the aqueous formaldehyde solution of step C     comprises about 35 to about 85 weight percent formaldehyde, based on     the total weight of the aqueous formaldehyde solution;     and wherein the process further comprises -   (D) contacting the aqueous raffinate phase from step (B) with a wash     solvent comprising about 80 to about 100 weight percent, based on     the total weight of the wash solvent, of a wash diluent comprising     hexane, heptane, decane, methylcyclohexane, benzene, toluene,     xylene, or a combination thereof; and about 0 to about 20 weight     percent of a wash modifier comprising 2-ethylhexanoic acid, lauric     acid, bis(2-ethylhexyl)hydrogen phosphate, 2-ethylhexanol,     2-ethylbutanol, n-hexanol, n-octanol, n-decanol, or a combination     thereof, to form a washed aqueous raffinate phase and an organic     wash extract phase, wherein the weight ratio of the wash solvent to     the aqueous raffinate phase is about 0.1:1 to about 1:1; -   (E) separating the washed aqueous raffinate and organic wash extract     phases; and -   (F) combining the organic wash extract phase with the extraction     solvent of step (A) or with the organic extract phase of step (B).

A process that includes the embodiments of paragraph [0060], wherein

the aqueous glycolic acid mixture is prepared by process comprising the carbonylation of formaldehyde in the presence of a sulfuric acid catalyst;

the aqueous formaldehyde solution of step (C) comprises about 40 to about 55 weight percent formaldehyde and the aqueous formaldehyde extract of step (C) is passed to the glycolic acid process;

the acid catalyst comprises sulfuric acid; the tertiary amine comprises tris(2-ethylhexyl)amine; the modifier comprises 2-ethylhexanoic acid;

the diluent comprises hexane, heptane, decane, or a combination thereof; the wash solvent comprises hexane, heptane, decane, or a combination thereof; the wash modifier comprises 2-ethylhexanoic acid, n-hexanol, n-decanol, or a combination thereof; and the weight ratio of the modifier to the tertiary amine is about 2:1 to about 4:1; and

the aqueous formaldehyde extract comprises about 0.5 to about 10 weight percent sulfuric acid, based on the total weight of the aqueous formaldehyde extract.

The principles laid out in the instant invention are further illustrated by the following examples.

EXAMPLES

General—Glycolic acid solutions and extraction samples were analyzed by liquid chromatography. Quantitation of analytes comprising glycolic acid, glycolate oligomers, and related secies was performed using ion-exclusion chromatography after samples were subjected to acid hydrolysis in aqueous 25% v/v H₂SO₄ at 80° C. for 30 minutes. The analytes were separated on a Hamilton PRP X300 column using a 10 mM H₃PO₄ mobile phase with a 1-20% v/v acetonitrile gradient. The eluting components were monitored using a UV detector set at 210 nm and their concentrations calculated based on calibration using external standards. Formaldehyde was determined by liquid chromatographic separation of the 2,4-dinitrophenylhydrazone derivative of formaldehyde and its subsequent detection by UV at 360 nm. The same acid hydrolysate from the procedure above was reacted with dinitrophenylhydrazine, then analyzed using a Phenomenex Luna C8 column using a 1:1 water:acetonitrile mobile phase under isocratic conditions. The formaldehyde concentration was calculated based on calibration using external standards.

Reactor effluent and extraction samples also were analyzed for sulfur using a wavelength dispersive x-ray fluorescence (WDXRF) semi-quantitative application called UNIQUANT™ (UQ). UQ affords standardless XRF analysis of samples. The data were mathematically corrected for matrix differences between calibration standards and samples as well as absorption and enhancement effects; i.e. inter-element effects. Instrument conditions for sulfur analysis were: Line, K_(a); kV, 40; mA, 60; Filter, none; Collimator Spacing (mm), 150; Crystal, Ge III-C; Peak Angle (2q), 110.6712; Detector, flow; PHD Lower, 35; PHD Upper, 70; Collimator Mask (mm), 30; Peak time (s), 30.

Extractor samples were diluted in isopropyl alcohol to minimize matrix effects and analyzed quantitatively using WDXRF. The WDXRF calibrations were performed using serial dilutions of stock standards prepared wt./wt. and certified using ICP-OES. Instrument conditions for sulfur analysis were: Line, K_(a); kV, 50; mA, 60; Filter, none; Collimator Spacing (mm), 700; Crystal, Graphite; Peak Angle (2q), 106.4608; —offset, 2.6696; Detector, flow; PHD Lower, 27; PHD Upper, 75; Collimator Mask (mm), 30; —Offset time (s), 10; Peak time (s), 50.

For all extraction examples, the molar selectivity for the tertiary amine-containing phase (i.e., extraction solvent) for sulfuric acid (H₂SO₄) over glycolic acid (GA) is defined as follows:

${{Molar}\mspace{14mu}{Selectivity}} = \frac{\begin{matrix} {\left( {{Moles}\mspace{14mu} H_{2}{SO}_{4}\mspace{14mu}{in}\mspace{14mu}{amine}\mspace{14mu}{phase}} \right) \times} \\ \left( {{Moles}\mspace{14mu}{GA}\mspace{14mu}{in}\mspace{14mu}{aqueous}\mspace{14mu}{GA}\mspace{14mu}{Phase}} \right) \end{matrix}}{\begin{matrix} {\left( {{Moles}\mspace{14mu} H_{2}{SO}_{4}\mspace{14mu}{in}\mspace{14mu}{{aq}.\mspace{14mu}{GA}}\mspace{14mu}{phase}} \right) \times} \\ \left( {{Moles}\mspace{20mu} H_{2}{SO}_{4}\mspace{14mu}{in}\mspace{14mu}{amine}\mspace{14mu}{Phase}} \right) \end{matrix}}$ Throughout the examples, the following abbreviations are used in the Tables:

-   -   HFr=formaldehyde     -   GA=glycolic acid and oligomers     -   HOFr=formic acid     -   DGA=diglycolic acid     -   MAA=methoxyacetic acid     -   TfOH=trifluoromethanesulfonic acid or triflic acid     -   PFOA-H=perfluorooctanoic acid     -   TEHA=tris(2-ethylhexyl)amine     -   2-EHA=2-ethylhexanoic acid     -   DEHPA=bis(2-ethylhexyl)hydrogen phosphate     -   MTSA=methanetrisulfonic acid

Examples 1-4 Preparation of Aqueous Glycolic Acid Solutions

Hydrocarboxylation reactor effluents were prepared for subsequent extraction experiments in the following manner for Examples 1-4: A mixture comprising formaldehyde, water, glycolic acid, and acid catalyst was fed continuously to a high pressure zirconium autoclave, nominally 125 mL volume, fitted with a hollow shaft Rushton turbine impeller (for gas introduction and dispersion), baffles, thermo well, gas inlet tube, and sip tube to maintain liquid level at approximately 90 mL and to provide an exit for product effluent. The autoclave was heated electrically by a band heater, with temperature control provided by feedback via a K-type thermocouple in the autoclave thermo well. Pure carbon monoxide gas (>99.9%) was fed to the autoclave via a Brooks flow controller. Reactor effluent passed through zirconium tubing, maintained at 60° C., an automatic pressure control valve, and into a Hastelloy collection vessel (1 liter), also maintained at 60° C. The collection vessel was drained every six hours and analyzed by liquid chromatography, gas chromatography, and X-ray sulfur analysis to determine product composition. If conditions of feed flow rate, reactor temperature or pressure, gas flow rate, agitation rate were changed, the reactor was assumed to be at steady state operation after 6 to 10 reactor volumes of feed had been passed through the reactor. Feed conditions and product analyses are given in Table 1 and Table 2 respectively.

TABLE 1 Reaction Conditions for the Preparation of Glycolic Acid Molar Ratios in Feed Residence Glycolic HFr Example T, ° C. P, bara time, min Acid (as 100% HFr) Water Acid Catalyst 1 180 135 92 2.0 1.0 1.0 0.10 (H₂SO₄) 2 190 132 92 2.0 1.0 1.4 0.10 (H₂SO₄) 3 190 132 92 2.0 1.0 2.2 0.09 (H₂SO₄) 4 205 180 55 2.0 1.0 2.2 0.09 (TfOH)

TABLE 2 Analysis of Glycolic Acid Reaction Mixtures Weight % Species in Reactor Effluent % Molar Sum of % HFr HFr DGA, Con- Selectivity HOFR, Acid Example version to GA GA HFr MAA Catalyst 1 92.0% 93.6% 88.6% 0.9% 1.7% 3.3% 2 93.1% 87.0% 84.6% 0.8% 2.0% 4.0% 3 90.0% 84.5% 80.8% 1.3% 1.9% 3.9% 4 94.2% 89.2% 80.3% 0.66%  1.5% 3.1%

Example 5

The reactor effluent generated in Example 1, comprising 3.3 wt % sulfuric acid in crude aqueous glycolic acid, was subjected to a series of twenty-four cross-flow batch extractions using the following procedure to simulate a six-stage continuous countercurrent extraction process with the reactor effluent feed on stage one and the extraction solvent mixture introduced on stage six. The reactor effluent generated in Reaction Example 1, comprising 3.3 wt % sulfuric acid in crude aqueous glycolic acid, was subjected to a cascaded series of twenty-four cross-flow batch extractions to simulate a six-stage continuous countercurrent extraction process, with the reactor effluent feed on stage one, and the amine solvent mixture introduced on stage six. The multi-cycle, cascaded pattern of 24 extractions in which multiple fresh feed and solvent charges are introduced at separate ends of each cycle of the cascade, and with raffinate and extract compositions introduced to the next cycle of the cascade, results in a set of conditions on the final cycle which have been shown to closely approach the equilibrium composition profile of a continuous, staged countercurrent extractor. For this work, with the relatively high partition coefficient of sulfuric acid into the amine solvent mixture, three cycles were found to be sufficient to asymptotically approach continuous extraction equilibrium conditions. The simulated countercurrent extraction technique used herein is well-known to those skilled in the art and is laid out in detail in Treybal, Liquid Extraction, 2^(nd) Ed., McGraw-Hill, New York, N.Y., 1963, pp. 349-366.

The pattern of 24 extractions results in a final set of conditions which have been shown to closely approach the equilibrium composition profile of a continuous six stage countercurrent extractor. The extraction solvent comprised a mixture of 35 wt % tris(2-ethylhexyl)amine (“TEHA”), 32.5 wt % 2-ethylhexanoic acid (“2-EHA”), and 32.5 wt % heptane. The solvent to feed weight ratio was 0.5:1. The final simulated extract and raffinate streams were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the products. None of the extractions exhibited the formation of three liquid phases. The recovery of the sulfuric acid from the hydrocarboxylation reactor effluent to the organic extract product was 92.3%, and 95.2% of the feed glycolic acid was recovered in the raffinate. The molar selectivity of the extraction solvent for sulfuric acid over glycolic acid was 19.3.

Example 6

The reactor effluent generated in Example 1 was subjected to a series of twenty-four cross-flow batch extractions using the same procedure of Example 5 to simulate a six-stage continuous countercurrent extraction process, with the reactor effluent feed on stage one, and the extraction solvent mixture introduced on stage six. The extraction solvent comprised a mixture of 35 wt % tris(2-ethylhexyl)amine, 32.5 wt % 2-ethylhexanoic acid, and 32.5 wt % heptane. The extraction solvent to feed weight ratio was 0.67:1.0. The final simulated extract and raffinate streams were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the products. None of the extractions exhibited the formation of three liquid phases. The recovery of the sulfuric acid from the hydrocarboxylation reactor effluent to the organic extract phase was 98.1%; 99.2% of the feed glycolic acid in the reactor effluent was recovered in the raffinate. The molar selectivity of the extraction solvent for sulfuric acid over glycolic acid was 119.4.

Example 7

The reactor effluent generated in Example 2, comprising 4.0 wt % sulfuric acid in crude aqueous glycolic acid, was subjected to a series of twenty-four cross-flow batch extractions at 40° C. using the procedure laid out in Example 5 to simulate a six-stage continuous countercurrent extraction process, with the reactor effluent feed on stage one, and the extraction solvent mixture introduced on stage six. The extraction solvent contained a mixture of 35 wt % tris(2-ethylhexyl)amine, 32.5 wt % bis(2-ethylhexyl)hydrogen phosphate (“DEHPA”) and 32.5 wt % heptane. The extraction solvent to feed weight ratio was 0.67:1.0. The final extract and raffinate streams were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the products. None of the extractions exhibited the formation of three liquid phases. The recovery of the sulfuric acid from the hydrocarboxylation reactor effluent to the organic extract phase was 98.5%; 95.7% of the feed glycolic acid was recovered in the raffinate. The molar selectivity of the extraction solvent for sulfuric acid over glycolic acid was 23.2.

Example 8 Back extraction simulation with DEHPA and HFr

The reactor effluent generated in Example 2, comprising 4.0 wt % sulfuric acid in crude aqueous glycolic acid, was subjected to a single cross flow extraction with an extraction solvent containing 35 wt % tris(2-ethylhexyl)amine, 32.0 wt % bis(2-ethylhexyl)hydrogen phosphate and 33.0 wt % heptane. The extraction solvent to feed weight ratio was 0.45:1.0. This extraction recovered 64% of the sulfuric acid that was present in the aqueous glycolic acid feed into the organic extract phase. The organic extract phase from the cross flow extraction, containing 6.2 weight % H₂SO₄ as a tertiary amine-acid complex, was then subjected to a series of twenty-four cross-flow batch extractions at 75° C. using the procedure set for in Example 5 to simulate a six-stage continuous countercurrent extraction process with the organic extract phase on stage one, and aqueous formaldehyde solution introduced on stage six. The formaldehyde solution was a mixture of 42 wt % formaldehyde in water, generated by the partial oxidation of methanol over a commercial mixed metal oxide formaldehyde catalyst. The formaldehyde solution extractant to feed weight ratio was 0.67:1.0. The final simulated extract and raffinate streams were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the products. None of the extractions exhibited the formation of three liquid phases. The recovery of the sulfuric acid from the organic extract phase to the aqueous formaldehyde extract was 98.7%. The sulfuric acid content of the organic raffinate phase was 820 ppm after extraction and the concentration of sulfuric acid in the aqueous formaldehyde extract phase was 4.3 wt %. About 0.5% of the formaldehyde in the original formaldehyde feed was extracted into the organic raffinate phase.

Example 9

The reactor effluent generated in Example 3, comprising 3.9 wt % sulfuric acid in crude aqueous glycolic acid, was subjected to a cross-flow batch extraction at 40° C. using an extraction solvent containing a mixture of 30 wt % tris(2-ethylhexyl)amine, 25 wt % bis(2-ethylhexyl)hydrogen phosphate and 45 wt % heptane. The extraction solvent to feed weight ratio was 1.0:1.0. The organic extract phase from this extraction was set aside and the glycolic acid-rich aqueous raffinate phase was extracted with an additional equal portion of fresh extraction solvent. This procedure was repeated two additional times with equal portions of fresh extraction solvent for a total of four cross-flow extractions. The final organic extract and aqueous raffinate phases were subjected to liquid chromatography, gas chromatography, and X-ray sulfur and phosphorus analyses to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. The concentration of sulfuric acid in the final aqueous raffinate phase was less than the analytical detection limit, indicating essentially 100% removal of the sulfuric acid from the hydrocarboxylation reactor effluent in four cross flow extractions.

Example 10

This example illustrates the recovery of the tertiary amine and modifier from the glycolic acid-rich aqueous raffinate phase by washing with additional diluent. The glycolic acid-rich aqueous raffinate phase from the fourth cross-flow extraction generated in Example 5, containing 1.0 wt % TEHA and 1.13 wt % DEHPA, was subjected to a cross-flow batch extraction at 40° C. using a heptane as the wash solvent. The wash solvent to aqueous feed weight ratio was 1.0:0.77. The organic wash extract from this extraction was set aside and the washed aqueous raffinate phase was extracted with an additional equal portion of fresh wash solvent. This was repeated two additional times with equal portions of fresh wash solvent for a total of four cross-flow extractions. The final organic wash extract and washed aqueous raffinate phases were subjected to gas chromatography and X-ray phosphorus analysis to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. The concentrations of TEHA and DEHPA in the final washed aqueous raffinate phase were 0.01 wt % and 1.03 wt %, indicating 99% and 7% recovery, respectively, in four cross flow extractions.

Example 11

This example illustrates the effect of the ratio of modifier to tertiary amine and diluent on the extraction of sulfuric acid from hydrocarboxylation reactor effluent. The reactor effluent generated in Example 3 was subjected to a series of cross-flow batch extractions at 40° C. using a extraction solvent containing 50 wt % of a mixture of tris(2-ethylhexyl)amine, 2-ethylhexanoic acid and 50 wt % of a diluent of either heptane or decane. Four cross flow extractions were completed for each extraction solvent mixture with the reactor effluent. The reactor effluent was extracted with the specified extraction solvent mixture at the given solvent to feed ratio, and the resulting aqueous raffinate phase from first extraction was contacted with a portion of fresh extraction solvent. This sequence was repeated an additional two times for a total of four cross flow extractions. The organic extract and aqueous raffinate phases from each cross flow extraction were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the phases. The solvent to feed conditions for each set of extractions, and the resulting sulfuric acid recovery into the extract phase, glycolic acid recovery in the raffinate, and overall molar selectivity of sulfuric acid to glycolic acid are summarized in Table 3 below.

TABLE 3 % % Glycolic 2-EHA/ H₂SO₄ Acid (GA) Molar TEHA S/F S/F Recov Recovery Selectivity Wt Extr Extr to to of H₂SO₄ Ex. Ratio Diluent #1 #2-#4 Extract Raffinate over GA 11-1 1.0 Heptane 0.50 0.5 97.8% 96.8% 30.3 11-2 2.0 Heptane 0.50 0.16 94.2% 98.0% 46.8 11-3 3.0 Heptane 0.50 0.16 87.3% 98.3% 50.4 11-4 3.0 Decane 0.50 0.16 91.8% 98.0% 45.1

Example 12

This example illustrates the back extraction of sulfuric acid from the sulfuric acid-loaded organic extract phase into aqueous formaldehyde. The sulfuric acid-rich organic extract phase from the first cross-flow extraction generated in Example 11-1 contained 6.1 weight percent sulfuric acid. This mixture was subjected to cross-flow batch extractions at 75° C. using 48 wt % formaldehyde in water. The solvent to feed weight ratio in each case was 0.5:1.0. After each extraction, the aqueous formaldehyde extract was set aside and the organic raffinate phase was extracted with an additional equal portion of fresh 48 wt % aqueous formaldehyde solution. This procedure was repeated four times with equal portions of fresh solvent for a total of five cross-flow extractions. The final extract and raffinate phases were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. Ninety percent of the sulfuric acid in the organic extract was recovered in the aqueous formaldehyde extract phase in five cross flow extractions.

Example 13

This example illustrates the recovery of tertiary amine and modifier from the glycolic acid-rich aqueous raffinate phase by washing with additional solvents. The glycolic acid-rich aqueous raffinate phase from the fourth cross-flow extraction generated in Example 11-1 contained 2.56 wt % TEHA and 0.59 wt % 2-EHA. This mixture was divided into three parts and each part was subjected to cross-flow batch extractions at 40° C. using three different wash solvent compositions. The wash solvent to feed weight ratio in each case was 0.4:1.0. After each extraction, the organic wash extract was set aside and the washed aqueous raffinate was extracted with an additional equal portion of fresh wash solvent. This procedure was repeated three times with equal portions of fresh wash solvent for a total of four cross-flow extractions. The final organic wash extract and washed aqueous raffinate streams were subjected to gas chromatography to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. The concentrations and % recovery of TEHA and 2-EHA in the final washed aqueous raffinate phase are summarized in Table 4 below.

TABLE 4 wt % TEHA wt % 2-EHA in Final % Recovery in Final % Recovery Extractant Raffinate of TEHA Raffinate of 2-EHA 100 wt % 0.042% 98.4% 0.011% 98.1% Heptane 90 wt % 0.018% 99.3% 0.000% 100.0% Heptane, 10 wt % 2-Ethylhexanol 90 wt % 0.037% 98.6% 0.000% 100.0% Heptane, 10 wt % n-hexanol

Example 14 Back Extraction of Acid Catalyst

This example illustrates the effect of modifier to tertiary amine weight ratio, percent formaldehyde, and the concentration of diluent on the back extraction of sulfuric acid from the sulfuric acid-loaded organic extract phase into aqueous formaldehyde. The sulfuric acid-rich organic extract phase from the first cross-flow extraction generated in Examples 11-2 and 11-3 were subjected to cross-flow batch extractions at 75° C. using an aqueous formaldehyde solution as the extraction solvent. The solvent to feed weight ratio in each cross flow extraction was 0.35:1.0. After each extraction, the aqueous formaldehyde extract was set aside and the organic raffinate phase was extracted with an additional equal portion of fresh aqueous formaldehyde solution. This procedure was repeated with equal portions of fresh solvent for a total of three cross-flow extractions. The final aqueous formaldehyde extract and organic raffinate phases were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. Feed and product specifications are given in Table 5 below.

TABLE 5 % H₂SO₄ Extracted into Formal- Source EHA/TEHA Wt % Wt % wt % dehyde of Wt Ratio Heptane Formaldehyde H₂SO₄ after Three Feed in Feed in Feed Solvent in Feed Extractions 11-2 2 50% 48% 4.4% 71.4% 11-2 2 50% 35% 4.4% 92.2% 11-2 2 50% 20% 4.4% 97.1% 11-2 2 50%  0% 4.4% 98.6% 11-2 2 67% 48% 4.4% 95.6% 11-2 2 67% 35% 4.4% 98.9% 11-2 2 67% 20% 4.4% 99.2% 11-2 2 67%  0% 4.4% 99.3% 11-3 3 50% 48% 3.2% 85.3% 11-3 3 50% 35% 3.2% 95.3% 11-3 3 50% 20% 3.2% 97.9% 11-3 3 50%  0% 3.2% 98.8% 11-3 3 67% 48% 3.2% 98.3% 11-3 3 67% 35% 3.2% 98.8% 11-3 3 67% 20% 3.2% 98.9% 11-3 3 67%  0% 3.2% 98.9%

Example 15 Recovery of Tertiary Amine and Modifier

This example illustrates the recovery of tertiary amine and modifier from the glycolic acid-rich aqueous raffinate phase by washing with additional solvent. The glycolic acid-rich aqueous raffinate phases from the fourth cross-flow extraction generated in Examples 11-2, 11-3, and 11-4 were subjected to cross-flow batch extractions at 40° C. The wash solvent to feed weight ratio in each case was 0.4:1.0. After each extraction, the organic wash extract was set aside and the washed aqueous raffinate was extracted with an additional equal portion of fresh wash solvent. This procedure was repeated three times with equal portions of fresh wash solvent for a total of five cross-flow extractions. The final organic wash extract and washed aqueous raffinate streams were subjected to gas chromatography to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. The concentrations and % recovery of TEHA and 2-EHA in the final raffinate phases are summarized in Table 6 below.

TABLE 6 EHA/TEHA wt % TEHA wt % 2-EHA Source Wt Ratio in in Final % Recov in Final % Recov of Feed Feed Wash Solvent Raffinate TEHA Raffinate 2-EHA 11-2 2 100 wt % Heptane 0.230% 84.0% 0.018%   96.4% 11-3 3 100 wt % Heptane 0.091% 93.7% 0.0% 100.0% 11-4 2 100 wt % Decane 0.010% 99.3% 0.0% 100.0%

Example 16

This example illustrates compositions that lead to the formation of three liquid phases for an extraction solvent containing a diluent, 2-ethylhexanoic acid, and TEHA. A solution of aqueous glycolic acid and sulfuric acid was prepared by mixing crystalline glycolic acid, 98 wt % sulfuric acid, with sufficient water to give a solution containing 11.1 wt % sulfuric acid, 75.7 wt % glycolic acid, and 13.2 wt % water. This solution was contacted in a 1:1 weight ratio with mixtures containing 1:1, 2:1, and 3:1 mass ratios of 2-EHA:TEHA at 40° C., 80° C., or 100° C. The resulting mixtures separated into two liquid phases upon settling. Temperature was maintained, and an alkane diluent (either heptane or decane) was added until the onset of the formation of three liquid phases. Results are summarized in Table 7.

TABLE 7 Amount of Alkane Required to Cause Three-Phase Formation Weight Weight % Weight % EHA/ % EHA/ Aqueous Alkane TEHA TEHA Glycolic Acid Added to Mass Mix & H₂SO₄ Form Three Ratio T (° C.) Added Mix Added Diluent Phases 1.00 40.0 19.7% 19.7% heptane 60.6% 1.00 80.0 21.8% 21.8% heptane 56.4% 1.98 40.0 11.75%  11.75%  heptane 76.5% 1.99 80.0 13.9% 13.9% heptane 72.2% 3.00 40.0 9.75% 9.75% heptane 80.5% 3.00 80.0 10.15%  10.15%  heptane 79.7% 1.99 40.0 15.8% 15.8% decane 68.4% 1.99 100.0 21.8% 21.8% decane 56.4%

Example 17 Effect of Diluents on 3 Phase Formation

This example illustrates which extraction solvent compositions lead to the formation of one, two, or three phases during the extraction of sulfuric acid from aqueous glycolic acid mixtures. A solution of 85 wt % glycolic acid in water was mixed with concentrated (98 wt %) sulfuric acid to give mixtures comprising 1%, 3%, 6%, 12%, 24%, and 33% by weight sulfuric acid in aqueous glycolic acid. Likewise, mixtures of tris(2-ethylhexyl)amine in various diluent and modifier mixtures were prepared as shown in Table 8A. The weight percentages for the diluent and modifier are for the combined diluent-modifier solution before the addition of the tertiary amine. The weight percentages of the tertiary amine indicate the weight percentage of the tertiary in the final extraction solvent composition. For example, in Example 17-1, the final extraction solvent composition contains 35 wt % TEHA and 65 wt % n-octanol. A portion of each extraction solvent was contacted with an equal mass of each of the sulfuric acid-aqueous GA mixtures in a glass vial, mixed, allowed to equilibrate, and to separate into multiple phases by holding at 40° C. or 80° C. The loss of glycolic acid into the extract phase was calculated for point one in each set of data. The sulfuric acid concentrations and the corresponding extraction are similar to equilibrium points that would be seen across a continuous countercurrent extractor. Thus, if three-phase or two-phase formation is observed in any of the samples, then such behavior most likely would occur in a continuous countercurrent extractor. The number of phases formed at each condition and the corresponding loss of glycolic acid into the amine phase at point one of each set of data is given in Table 8B. Examples 17-22 and 17-23 in Table 8B showed a 3-5 wt % loss of diluent into the aqueous glycolic acid phase.

TABLE 8A Extraction Conditions Exam- Temp Wt % Wt % Wt % ple ° C. TEHA Modifier Diluent Modifier Diluent 17-1 40   35% n-Octanol 100% 17-2 40   35% 2-ethylhexanol 100% 17-3 40 35.0% 2-ethylhexanol heptane 50% 50% 17-4 40 34.9% 2-ethylhexanol heptane 20% 80% 17-5 40 43.7% 2-ethylhexanol heptane 20% 80% 17-6 40 52.3% 2-ethylhexanol heptane 21% 79% 17-7 40   35% Heptane 100% 17-8 40   35% 2-heptanone 100% 17-9 40   35% 2-heptanone Heptane 50% 50% 17-10 40 C.   35% 2-EHA 100% 17-11 40 C.   35% 2-EHA Heptane 50% 50% 17-12 40 C. 35.0% 2-EHA heptane 50% 50% 17-13 40 C. 35.0% 2-EHA heptane 20% 80% 17-14 40 C. 43.8% 2-EHA heptane 20% 80% 17-15 40 C. 52.4% 2-EHA heptane 20% 80% 17-16 40 C.   35% Lauric acid 100% 17-17 40 C.   35% Dibutyl Ether 100% 17-18 40 C.   35% Toluene 100% 17-19 40 C. 52.5% 2-EHA Heptane 50% 50% 17-20 40 C. 17.5% 2-EHA Heptane 50% 50% 17-21 40 C. 35.0% 5-ethyl-2- 100% nonanone 17-22 40 C. 34.8% 5-ethyl-2- heptane 50% 50% nonanone 17-23 40 C. 35.0% 5-ethyl-2- heptane 20% 80% nonanone 17-24 40 C. 21.3% 2-EHA Heptane 50% 50% 17-25 40 C. 21.3% n-Decanol Heptane 50% 50%

TABLE 8B Results of Extraction Number of Phases Present After Extraction % GA Loss Point 1 - Point 2 - Point 3 - Point 4 - Point 5 - Point 6 - to Amine 1% 3% 6% 12% 24% 33% Phase at Example H₂SO₄ H₂SO₄ H₂SO₄ H₂SO₄ H₂SO₄ H₂SO₄ Point 1 17-1 1 1 2 2 100%  17-2 2 2 2 2 15%  17-3 2 3 3 2 2 2 9.2%   17-4 2 3 3 3 3 3 3.4%   17-5 2 3 3 3 3 3 3.2%   17-6 2 2 3 3 3 3 0% 17-7 2 3 3 3 0% 17-8 1 1 1 2 100%  17-9 2 3 3 3 10%  17-10 2 2 2 2 2 2 13%  17-11 2 2 2 2 2 2 0% 17-12 2 2 2 2 2 2 4.2%   17-13 2 2 3 3 3 3 0.5%   17-14 2 2 3 3 3 3 0.7%   17-15 2 2 3 3 3 3 0% 17-16 2 2 2 2 0% 17-17 2 3 3 3 32%  17-18 2 3 3 3 0% 17-19 2 2 2 2 2 2 0% 17-20 2 2 2 2 2 2 0% 17-21 2 2 2 2 2 2 5% 17-22 2 2 3 3 3 3 3-5% 17-23 2 2 3 3 3 3 3-5% 17-24 2 2 2 2 2 2 0%

Example 18 Extraction of Methanetrisulfonic Acid

This example illustrates the effect of the ratio of modifier to tertiary amine for the extraction of methane trisulfonic acid (“MTSA”) from hydrocarboxylation reactor effluent. The aqueous reactor effluent generated in Example 4 was subjected to a series of cross-flow batch extractions at 40° C. using a extraction solvent containing 50 wt % of a mixture of tris(2-ethylhexyl)amine, 2-ethylhexanoic acid and 50 wt % heptane as a diluent. Three cross flow extractions were completed for each extraction solvent mixture with the reactor effluent. The reactor effluent was extracted with the specified extraction solvent mixture and the resulting aqueous glycolic acid phase from first extraction was contacted with a portion of fresh extraction solvent. This sequence was repeated an additional time for a total of three cross flow extractions. The solvent to feed ratio was 0.5:1 in the first extraction and 0.16:1 for extractions 2-4. The organic extract and aqueous raffinate phases from each cross flow extraction were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the phases. The feed conditions for each set of extractions, and the resulting MTSA recovery into the organic extract phase, glycolic acid recovery in the aqueous raffinate, and overall molar selectivity of MTSA to glycolic acid are summarized in Table 9 below.

TABLE 9 % Glycolic Molar EHA/ % MTSA Acid (GA) Selectivity TEHA Wt % Recov to Recovery to of MTSA Example Ratio Diluent Extract Raffinate over GA 18-1 3.0 50% 96.2% 98.5% 65.0 18-2 2.0 50% 97.4% 99.0% 101.0

Example 19 Back Extraction of Methanetrisulfonic Acid

This example illustrates the effect of modifier to tertiary amine weight ratio and concentration of diluent on the back extraction of methanetrisulfonic acid from the MTSA-loaded organic extract phase into aqueous formaldehyde. The MTSA-rich extract phase from the first cross-flow extraction generated in Example 18-2 was subjected to cross-flow batch extractions at 75° C. using an aqueous formaldehyde solution as the extraction solvent at the solvent to feed ratio indicated in Table 10. After each extraction, the organic extract phase was set aside and the aqueous raffinate phase was extracted with an additional equal portion of fresh aqueous formaldehyde solution. This procedure was repeated with equal portions of fresh solvent for a total of three cross-flow extractions. The final extract and raffinate phases were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. Feed and product specifications are given in Table 10 below.

TABLE 10 % MTSA Extracted into Wt % Wt % wt % Formaldehyde Source of EHA/TEHA Wt Heptane in Formaldehyde H₂SO₄ in S/F Phase after 3 Feed Ratio Feed Feed Solvent Feed Ratio Extractions 18-2 2 50% 38.5% 3.41% 0.35 50.1% 18-2 2 50% 28.1% 3.41% 0.35 67.2% 18-2 2 50% 16.0% 3.41% 0.35 86.5% 18-2 2 50% 0.0% 3.41% 0.35 92.0% 18-2 2 67% 38.5% 3.41% 0.23 80.8% 18-2 2 67% 28.1% 3.41% 0.23 90.4% 18-2 2 67% 16.0% 3.41% 0.23 93.1% 18-2 2 67% 0.0% 3.41% 0.23 95.5%

Example 20 Recovery of Tertiary Amine and Modifier from Aqueous Raffinate

This example illustrates the recovery of the tertiary amine and modifier from the glycolic acid-rich aqueous raffinate phase by washing with additional solvent. The glycolic acid-rich raffinate phase from the fourth cross-flow extraction generated in Examples 14-1 and 14-2 were combined and subjected to cross-flow batch extractions at 40° C. The combined glycolic acid rich, raffinate phases contained 0.43 wt % TEHA and 0.39 wt % 2-ethylhexanoic acid. The solvent to feed weight ratio in each case was 0.4:1.0. After each extraction, the organic wash extract was set aside and the washed aqueous raffinate was extracted with an additional equal portion of fresh wash solvent. This procedure was repeated four more times with equal portions of fresh wash solvent for a total of six cross-flow extractions. The final organic wash extract and washed aqueous raffinate phases were subjected to gas chromatography to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. The concentrations and % recovery of TEHA and 2-EHA in the final raffinate phases are summarized in Table 11 below.

TABLE 11 wt % TEHA % wt % 2-EHA % Source Wash in Final Recovery in Final Recovery of Feed Solvent Raffinate of TEHA Raffinate of 2-EHA 18-1, 100 wt % 0.038% 92.0% None 100.0% −2 Heptane detected

Example 21 Extraction of Trifluoromethanesulfonic Acid (Triflic Acid)

This example illustrates the effect of the ratio of modifier to tertiary amine and diluent concentration on the extraction of triflic acid from aqueous glycolic acid. A mixture comprising 82.4 wt % glycolic acid, 14.6 wt % water, and 3.0 wt % triflic acid was subjected to a cross-flow batch extraction at 40° C. using two different extraction solvents containing a mixture of tris(2-ethylhexyl)amine, 2-ethylhexanoic acid, and heptane as diluent. Extraction conditions and results are given below in Table 12.

TABLE 12 Solvent EHA/ Solvent/ TEHA Feed % Triflic Wt Wt % Wt % Wt % Weight Recov to Example Ratio TEHA 2-EHA Heptane Ratio Extract 21-1 3.0 12.4% 37.3% 50.3% 1.45 99.4% 21-2 2.9 8.4% 24.8% 66.2% 1.50 98.3%

Example 22 Back Extraction of Triflic Acid

This example illustrates the effect of modifier to tertiary amine weight ratio and concentration of diluent on the back extraction of triflic acid from the triflic acid-loaded organic extract phase into aqueous formaldehyde solution. The triflic acid-rich, organic extract phases from the cross-flow extractions generated in Examples 21-1 and 21-2 were subjected to cross-flow batch extractions at 70° C. using aqueous formaldehyde as the extraction solvent at the solvent to feed ratio shown in Table 13. After each extraction, the aqueous formaldehyde extract was set aside and the organic raffinate phase was extracted with an additional equal portion of fresh aqueous formaldehyde solution. This procedure was repeated with equal portions of fresh solvent for a total of five cross-flow extractions. The final aqueous formaldehyde extract and organic raffinate streams were subjected to liquid chromatography and X-ray sulfur analysis to determine the compositions of the phases. None of the extractions exhibited the formation of three liquid phases. Feed and product specifications are given in Table 13 below.

TABLE 13 % Triflic Extracted into Wt % Wt % wt % Solvent Phase Source of EHA/TEHA Wt Heptane in Formaldehyde Triflic in S/F after Three Feed Ratio Feed Feed in Solvent Feed Ratio Extractions 21-1 3.0 50.3%   0% 2.00% 0.5 62.2% 21-2 2.9 66.2%   0% 1.90% 0.5 94.8% 21-1 3.0 50.3% 51.0%  2.2% 1.0 39.8% 21-2 2.9 66.2% 51.0% 2.00% 1.0 69.3%

Examples 23-35 Triflic Acid Extract with Perfluorooctanoic Acid Modifier

Cross-flow (“forward”) extractions were performed at 70° C. using 85 wt % or 95 wt % aqueous glycolic acid, an equal weight of heptane phase comprising 25-50 wt % heptane, tris(2-ethylhexyl)amine (“TEHA”) and perfluorooctanoic acid (“PFOAH”) (1.5-3.0 eq PFOAH:eq TEHA), and a variety of initial triflic acid loadings (0.025-4.0 eq:eq TEHA). Back (“reverse”) extractions were performed under similar conditions using 50 wt % aqueous formaldehyde. The triflic acid concentrations were determined by sampling both phases and analyzing the samples by x-ray fluoresence (XRF) or inductively-coupled plasma (ICP), using standard methods known in the art and are shown in Tables 14-15

Representative procedures for the forward and back extractions Trifluoromethanesulfonic acid (TfOH), perfluorooctanoic acid (PFOA-H) and 95% para-formaldehyde (HFr) were obtained from Sigma-Aldrich, tris(2-ethylhexyl)amine from TCI America, and GLYPURE™ glycolic acid from DuPont.

Example 23 Preparation of 95% Aqueous Glycolic Acid Solution

Glycolic acid (23.69 g) was combined with water (1.23 g) and warmed with stirring to 85° C. forming a clear, viscous solution. The solution was stable upon cooling to 70° C. over the time frame of the experiments.

Example 24 Preparation of [TEHA-PFOA] for Forward Extraction

Perfluorooctanoic acid (38.165 g, 92.17 mmol) was combined with tris(2-ethylhexyl)amine (16.48 g, 46.58 mmol) and heptanes (18.02 g), and warmed with stirring to 70° C. to form a clear, pink solution comprising 0.641 mol salt/kg and 0.627 mol free PFOA-H/kg.

Example 25 Preparation of [TEHA-PFOA] Salt Solution for Back Extraction

Perfluorooctanoic acid (24.466 g, 63.92 mmol) was combined with tris(2-ethylhexyl)amine (11.26 g, 31.96 mmol) and heptanes (37.73 g), and warmed with stirring to 70° C. to form a clear, pink solution comprising 0.424 mol salt/kg and 0.424 mol free PFOA-H/kg.

Example 26 Preparation of 50% Aqueous Formaldehyde Solution

Para-formaldehyde (49.964 g), water (45.331 g) and trifluoromethanesulfonic acid (93 mg, 0.620 mmol) were combined and stirred at 97° C. for 48 h. The solution remained homogeneous upon cooling to 70° C.

Examples 27-30 Forward Extraction of Trifluoromethanesulfonic Acid

A typical procedure for the forward extraction follows: Glycolic acid solution (10.928 g) was added to a vial followed by TfOH (993 mg, 6.62 mmol) and [TEHA-PFOA] salt solution (10.999 g, 7.051 mmol salt), all at 70° C. Examples 27-29 used an 85 wt % aqueous glycolic acid while Examples 29 and 30 used 95 wt % aqueous glycolic acid; the remaining examples used 85 wt % aqueous glycolic acid. The contents of the vial were thoroughly agitated, centrifuged, and allowed to separate into an upper organic layer and a lower aqueous layer. Each layer was sampled for XRF or ICP analysis for sulfur content. The aqueous layer was removed with a Pasteur pipette, added to a new vial, and weighed. The TfOH/glycolic acid solution was then repeatedly extracted by adding an equal weight of fresh salt solution to the raffinate layer and repeating the above steps. The results are shown in Table 14.

Examples 31-35 Back Extractions of Trifluoromethane Sulfonic Acid

A typical procedure for the back extraction of triflic acid from a solution of TEHA and PFOA in heptane follows: [TEHA-PFOA] salt solution (4.266 g, 1.81 mmol salt) was combined with TfOH (237 mg, 1.62 mmol) and 50% aqueous HFr (4.108 g), all at 70° C., in a vial, simulating the back extraction at a high level of TfOH loading. The contents of the vial were thoroughly agitated, centrifuged, and allowed to separate into an upper organic layer and a lower aqueous layer. Each layer was sampled for XRF or ICP analysis for sulfur content. Samples of the aqueous HFr layer were added to vials containing pre-weighed isopropanol to avoid precipitation of HFr upon cooling. The steps above were repeated for each back extraction by combining [TEHA-PFOA] salt solution, TfOH and 50% aqueous HFr in vials such that TfOH was loaded at 0.5, 0.25, 0.125, 0.05 and 0.025 equivalent to 1 equivalent salt. The results are shown in Table 15.

TABLE 14 Forward Extractions of Triflic Acid with PFOA Excess PFOA Dil. Extraction stage, wt % Triflic acid Ex (equiv) wt % Phase 1 2 3 4 5 6 7 27 1.0 50 Aq 2.881 1.618 0.727 0.334 0.113 0.051 0.020 Org 2.856 1.743 0.965 0.461 0.174 0.071 0.027 28 1.0 25 Aq 4.405 1.754 0.588 0.141 0.040 0.011 0.008 Org 4.486 2.745 1.308 0.460 0.116 0.015 0.004 29 0.5 25 Aq 2.292 0.207 — — — — — Org 7.017 2.250 — — — — — 30 1 25 Aq 3.182 0.781 0.089 0.010 — — — Org 5.569 2.634 0.671 0.098 — — —

TABLE 15 Back Extractions of Triflic Acid with PFOA Excess PFOA Dil. Extraction stage, wt % Triflic acid Ex (equiv) wt % Phase 1 2 3 4 5 6 31 1.0 50 Aq 0.219 0.111 0.111 0.096 — — Org 0.041 0.028 0.014 0.016 — — 32 1.0 50 Aq 3.452 2.076 1.131 0.935 — — Org 0.922 0.539 0.257 0.152 — — 33 1.0 25 Aq 6.748 3.588 1.871 0.971 — — Org 2.147 1.262 0.687 0.317 — — 34 2.0 50 Aq 13.933 9.395 4.752 2.724 — — Org 1.504 0.554 0.146 0.066 — — 35 1.0 50 Aq 4.868 2.527 1.444 0.787 0.365 0.197 Org 1.105 0.636 0.356 0.162 0.089 0.045

Examples 36-40 Forward Extractions of Sulfuric Acid in Continuous Column

For examples 36 through 48, continuous extraction experiments were carried out in a Karr column containing four jacketed glass column sections (15.9 mm inside diameter, each 501 mm in length) stacked on top of each other. Jacketed glass disengagement sections, 25.4 mm inside diameter and 200 mm in length, were attached to the top and bottom of the four extractor sections. The four column sections and two disengagement sections were joined together with Teflon O-ring gaskets (25 mm thickness) held together with bolted flanges to form the column body. Feed ports were fitted into each Teflon O-ring to allow change of feed locations. The total height of the resulting column was approximately 2.6 meters. Separate temperature-controlled heating baths were connected to the jacket of each disengagement zone and one bath to the combined four column sections to maintain the desired extraction temperature gradient.

Agitation in the column was supplied by an 3.2 mm diameter Hastelloy 276C impeller shaft fitted with seventy-seven Teflon plates, each with eight radial rectangular petals (to provide gaps for liquid flow paths), spaced 25 mm apart in the column sections. The impeller shaft was attached at the top of the extractor to an electric motor fitted with a concentric gear to convert rotational motion into reciprocal motion. The agitator stroke length (i.e., extent of vertical motion) was 19 mm, and varied from 200 to 350 strokes per minute.

Depending on the chosen continuous phase, the liquid-liquid phase interface was maintained in either the top or bottom disengagement section (in the top section if the less dense phase were continuous, bottom section if the more dense phase were continuous) by visual observation and manual manipulation of the underflow take-off pump.

Up to three feeds could be supplied to the column via piston pumps from independently temperature-controlled jacketed glass vessels of four liter, two liter, and two liter volumes, while the underflow (more dense) product and the top, overflow (less dense) product were collected in two-liter glass vessels. The top product collected by gravity overflow from the upper disengagement section, while the bottoms product flow was controlled by a variable rate piston pump.

For the following examples possible feed locations are designated as follows from the top of the column to the bottom:

F1: Feed location between top disengagement zone and 1st column section

F2: Feed location between 1^(st) and 2^(nd) column sections

F3: Feed location between 2^(nd) and 3^(rd) column sections

F4: Feed location between 3^(rd) and 4^(th) column sections

F5: Feed location between 4^(th) column section and bottom disengagement zone

Hydrocarboxylation reactor effluents containing sulfuric acid, glycolic acid, glycolate oligomers, and water were fed to the continuous Karr column described above and contacted with an extraction solvent comprising an amine, carboxylic acid, and hydrocarbon diluent, and optionally a wash solvent. The column was operated with the solvent as the continuous phase. Feed, solvent, and wash compositions, flow rates, feed locations, and temperature of the forward extraction experiments are summarized in Table 16. In each experiment, the column reached steady state within an hour and was run continuously for six to eight hours, with sampling occurring every one to two hours. Averaged recoveries of glycolate species, amine, carboxylic acid, and hydrocarbon to the raffinate product, and sulfuric acid to the extract product over the time of steady state operation are given in Table 17.

TABLE 16 Feed Conditions for Forward Extractions of Sulfuric Acid in Continuous Karr Column Operation Agit. Rate Feed Strokes/ Mass Flow Feed wt % wt % GA Ex T, ° C. min S/F Ratio g/min Location H₂SO₄ Oligomers wt % Water 36 70 350 1.14 13.3 F1 3.43% 82.2% 14.33% 37 70 325 1.14 13.3 F1 2.99% 72.9% 24.16% 38 45 325 1.13 13.3 F1 2.93% 82.8% 14.30% 39 40 206 1.13 13.3 F1 4.14% 79.1% 16.72% 40 45 300 0.76 13.3 F1 0.78% 82.5% 16.72% Solv. Solv. Wash Wash Flow Solvent Comp. Flow Wash Comp Ex. g/min Location TEHA 2-EHA Heptane mL/min Location Heptane 36 15.2 F5 10.11% 36.49% 53.40% none 37 15.2 F4 10.78% 37.39% 51.83% 6.9 F5 100.0% 38 15.2 F4  9.99% 36.96% 53.05% 6.9 F5 100.0% 39 15.2 F5 10.00% 36.13% 53.87% none 40 11.4 F5 10.73% 36.50% 52.77% none

TABLE 17 Results of Forward Extractions of Sulfuric Acid in Continuous Karr Column Operation TEHA/H₂SO₄ EHA/TEHA Glycolic Ex. molar ratio molar ratio H₂SO₄ Amine Heptane 2-EHA Oligomers 36 0.94 3.61 98.6% 97.7% 100.0% 99.3% 99.1% 37 1.14 3.47 99.3% 98.6% 100.0% 99.6% 98.9% 38 1.08 3.70 97.8% 98.4% 100.0% 98.8% 98.8% 39 0.76 3.61 80.3% 98.9% 100.0% 99.0% 99.0% 40 3.26 3.40 93.4% 90.0% 100.0% 97.0% 99.5%

Examples 41-42 Continuous Wash of Raffinate from Forward Extraction

For example 41, the sulfuric acid-lean raffinate of Example 36, comprising glycolic acid, glycolate oligomers, and water was contacted continuously with a heptane wash solvent as the continuous phase in the Karr column described above to remove additional 2-ethylhexanoic acid and TEHA. Similarly for Example 42, the raffinate from Example 39 was contacted with heptane in the continuous column to remove additional 2-ethylhexanoic acid and TEHA. Feed compositions, flow rates, feed locations, and temperature of the wash experiments are summarized in Table 18. In each experiment, the column reached steady state within an hour and was run continuously for six to eight hours, with sampling occurring every one to two hours. Averaged recoveries of TEHA, 2-ethylhexanoic acid, and heptane to wash extract product over the time of steady state operation are given in Table 19.

TABLE 18 Feed Conditions for Wash Extractions of Raffinates from Continuous Forward Extractions Agit Rate Feed Strokes/ Mass Flow Feed wt % wt % Wash Flow Wash Ex. T, ° C. min W/F Ratio g/min Location TEHA 2-EHA g/min Location 41 45 200 0.52 13.3 F1 0.17% 0.46% 6.9 F5 42 70 310 0.51 20.0 F1 0.62%  0.8% 6.9 F5

TABLE 19 Results of Wash Extractions of Raffinates from Continuous Forward Extractions Ex. Amine Heptane 2-EHA 41 91.6% 99.97% 93.1% 42 87.0%  99.9% 82.7%

Examples 43-48 Back Extractions of Sulfuric Acid-Rich Solvents in Continuous Column

Sulfuric acid-rich extracts comprising sulfuric acid, TEHA, 2-ethylhexanoic acid, and heptane derived from the forward extraction of hydrocarboxylation effluents were fed to the continuous Karr column at a temperature of 70° C. as described above and contacted with an aqueous formaldehyde extraction solvent (continuous phase). The sulfuric acid-rich extracts were introduced to the Karr column at location F5 and the aqueous formaldehyde solvent was introduced at location F1. Feed and solvent compositions, and flow rates of the forward extraction experiments are summarized in Table 20. In each experiment, the column reached steady state within an hour and was run continuously for six to eight hours, with sampling occurring every one to two hours. Averaged recoveries of TEHA, 2-ethylhexanoic acid, and heptane to the raffinate product, and glycolic acid and sulfuric acid to the formaldehyde extract product over the time of steady state operation are given in Table 21.

TABLE 20 Feed Conditions for Continuous Back Extractions with Aqueous Formaldehyde Agit. Rate Mass S/F Feed Flow Feed Wt % Ex. Feed Strokes/min Ratio g/min H₂SO₄ GA Olig. 43 sulfuric acid-rich 310 1.45 11.4 2.59% 0.93% extract 44 Extract Example 36 310 2.76 11.4 2.21% 0.45% 45 Extract Example 37 300 2.89 7.6 1.99% 0.49% 46 Extract Example 37 327 2.23 7.6 1.99% 0.49% 47 Extract Example 37 327 1.49 7.6 1.99% 0.49% 48 Extract Example 38 332 0.495 22.8 1.87% 0.51% Solvent Flow Ex. TEHA 2-EHA Heptane g/min Solv. wt % (aq. HFr) water 43 9.33% 36.5% 50.65% 16.5 49.00% 51% 44 7.38% 29.1% 60.89% 31.5 45.00% 55% 45 7.54% 26.3% 63.71% 22.0 42.00% 58% 46 7.54% 26.3% 63.71% 17.0 49.00% 51% 47 7.54% 26.3% 63.71% 11.3 42.00% 58% 48 7.41% 27.7% 62.49% 11.3 49.90% 50.1%  

TABLE 21 Results for Continuous Back Extractions with Aqueous Formaldehyde Recovery to Formaldehyde Extract Product Glycolic Recovery to Raffinate Product Ex. H2SO4 Oligomers Amine Heptane 2-EHA 43 98.4% 100.0% 98.8% 100.0% 95.3% 44 99.8% 100.0% 99.0% 100.0% 100.0% 45 99.4% 100.0% 100.0% 100.0% 94.7% 46 98.8% 100.0% 98.0% 100.0% 94.4% 47 98.8% 100.0% 98.0% 100.0% 94.4% 48 98.7% 99.8% 100.0% 99.5%

Example 49 Extraction of Sulfuric Acid from Aqueous Glycolic Acid

Sulfuric acid was added to a 85 wt % glycolic acid-15 wt % water mixture to produce a solution comprising 3 wt % sulfuric acid. Extraction solvents were prepared by mixing an amine and diluents(s) as specified in Table 22. Five grams of each amine solvent solution was mixed with five grams of the sulfuric acid-aqueous glycolic acid mixture and allowed equilibrate at the temperature specified in Table 22. If two phases resulted, samples of each phase were analyzed by x-ray for sulfur content and converted into a sulfuric acid concentration in each phase (grams of sulfuric acid per gram of amine phase and grams of sulfuric acid per gram of aqueous glycolic acid phase).

TABLE 22 Extraction of Sulfuric Acid from Aqueous Glycolic Acid Wt % Wt % Wt % Acid/ Acid/ Amine Diluent 1 Diluent 2 Amine D1 D2 T, ° C. Phases GA Amine TEHA n-Octanol none 35% 65% 0% 40 1 n/a TEHA 2-Ethylhexanol none 35% 65% 0% 40 2 0.0012 0.0290 TEHA Heptane none 35% 65% 0% 40 2 0.0132 0.0125 TEHA 2-Heptanone none 35% 65% 0% 40 1 n/a Alamine n-Octanol none 35% 65% 0% 40 2 0.0004 0.0286 336 Alamine 2-Ethylhexanol none 35% 65% 0% 40 2 0.0006 0.0290 336 Alamine Heptane none 35% 65% 0% 40 3 n/a 336 Alamine 2-Heptanone none 35% 65% 0% 40 2 0.0003 0.0288 336 TEHA 2-EHA none 35% 65% 0% 40 2 0.0012 0.0260 TEHA 2-EHA Heptane 35% 32.5%   32%  40 2 0.0019 0.0264 TEHA Lauric acid none 35% 65% 0% 40 2 0.0011 0.0244 TEHA 2-Heptanone Heptane 35% 32.5%   32%  40 3 n/a TEHA Dibutylether none 35% 65% 0% 40 3 n/a TEHA Toluene none 35% 65% 0% 40 3 n/a Alamine 2-EHA none 35% 65% 0% 40 2 0.0005 0.0276 336 Alamine Toluene none 35% 65% 0% 40 2 0.0001 0.0278 336 TEHA 2-EHA none 35% 65% 0% 80 2 0.0017 0.0282 TEHA 2-EHA Heptane 35% 32.5%   32%  80 2 0.0055 0.0230 TEHA Lauric acid none 35% 65% 0% 80 2 0.0018 0.0198 TEHA 2-Heptanone Heptane 35% 32.5%   32%  80 3 n/a TEHA Dibutylether none 35% 65% 0% 80 3 n/a TEHA Toluene none 35% 65% 0% 80 3 n/a Alamine 2-EHA none 35% 65% 0% 80 2 0.0004 0.0281 336 Alamine Toluene none 35% 65% 0% 80 2 0.0001 0.0283 336 

We claim:
 1. A process for recovering an acid catalyst from aqueous glycolic acid, comprising (A) extracting an aqueous glycolic acid mixture, comprising (i) about 50 to about 95 weight percent glycolic acid, based on the total weight of the aqueous glycolic acid mixture, and (ii) about 0.2 to about 12 weight percent, based on the total weight of the aqueous glycolic acid mixture, of an acid catalyst comprising sulfuric acid, an alkyl sulfonic acid containing from 1 to 5 carbon atoms, a fluoroalkyl sulfonic acid containing from 1 to 5 carbon atoms, or a combination thereof; with an extraction solvent, comprising (i) about 5 to about 45 weight percent, based on the total weight of the extraction solvent, of at least one tertiary amine containing from 12 to 40 carbon atoms, at least one onium carboxylate compound, or a combination thereof; (ii) about 5 to about 45 weight percent of at least one modifier comprising an aliphatic carboxylic acid containing from 5 to 16 carbon atoms, a fluoroalkyl carboxylic acid containing 5 to 16 carbon atoms, an organophosphorus acid containing from 5 to 16 carbon atoms, or a combination thereof; and (iii) about 10 to about 90 weight percent of at least one diluent comprising carbon dioxide, an aliphatic hydrocarbon containing from 3 to 25 carbon atoms, an aromatic hydrocarbon containing 6 to 25 carbon atom, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof; to form an aqueous raffinate phase comprising a major amount of the glycolic acid contained in the aqueous glycolic acid mixture and an organic extract phase comprising a major amount of the acid catalyst contained in the aqueous glycolic acid mixture; (B) separating the aqueous raffinate and organic extract phases; and (C) extracting the organic extract phase from step (B) with an aqueous formaldehyde solution to form an aqueous formaldehyde extract comprising a major amount of the acid catalyst contained in the organic extract phase from step (B) and an organic raffinate phase comprising a minor amount of the acid catalyst contained in the organic extract phase.
 2. The process according to claim 1 wherein the aqueous glycolic acid mixture comprises about 70 to about 90 weight percent glycolic acid and is produced by contacting aqueous formaldehyde with carbon monoxide in the presence of an acid catalyst.
 3. The process according to claim 1 wherein the acid catalyst comprises sulfuric acid, trifluoromethanesulfonic acid, methanesulfonic acid, methanedisulfonic acid, methanetrisulfonic acid, bis(methylsulfonyl)methanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic acid, or a combination thereof.
 4. The process according to claim 3 wherein the tertiary amine comprises tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trioctylamine, triisooctylamine, triisodecyl amine, tridodecylamine, tridecylamine, dioctyldecylamine, didecyloctylamine, or a combination thereof.
 5. The process according to claim 4 wherein the modifier comprises n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, bis(2-ethylhexyl)hydrogen phosphate, perfluorooctanoic acid, or a combination thereof.
 6. The process according to claim 3 wherein the diluent comprises pentane, hexane, heptane, decane, methylcyclohexane, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, benzene, toluene, xylene, isoparaffinic mixed hydrocarbons having a boiling range between 90 and 325° C., or a combination thereof.
 7. The process according to claim 3 wherein the aqueous formaldehyde solution comprises about 35 to about 85 weight percent formaldehyde, the aqueous formaldehyde extract comprises about 0.5 to about 10 weight percent, based on the total weight of the aqueous formaldehyde extract, of the acid catalyst, and the weight ratio of the aqueous formaldehyde solution to the organic extract phase is about 0.1:1 to about 1:1.
 8. The process according to claim 5 wherein the acid catalyst comprises trifluoromethanesulfonic acid; the tertiary amine comprises tris(2-ethylhexyl)amine; and the modifier comprises perfluorooctanoic acid.
 9. The process according to claim 5 wherein the acid catalyst comprises sulfuric acid; the tertiary amine comprises tris(2-ethylhexyl)amine; the modifier comprises 2-ethylhexanoic acid, and the diluent comprises hexane, heptane, decane, or a combination thereof.
 10. The process according to claim 1 wherein steps (A) and (C) are carried out at a temperature of about 40 to about 85° C.
 11. The process according to claim 1 wherein the aqueous formaldehyde extract is passed to a process for the preparation of glycolic acid by carbonylation of formaldehyde in the presence of an acid catalyst.
 12. The process according to claim 1, further comprising extracting the aqueous raffinate phase from step (B) with a wash solvent comprising about 80 to about 100 weight percent, based on the total weight of the wash solvent, of a wash diluent comprising carbon dioxide, an aliphatic hydrocarbon containing from 3 to 25 carbon atoms, an aromatic hydrocarbon containing 6 to 25 carbon atoms, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof; and about 0 to about 20 weight percent of a wash modifier comprising an aliphatic carboxylic acid containing from 5 to 16 carbon atoms, an organophosphorus acid containing from 5 to 16 carbon atoms, an alkanol containing 6 to 12 carbon atoms, or a combination thereof, to form a washed aqueous raffinate phase and a organic wash extract phase, wherein the weight ratio of the wash solvent to the aqueous raffinate phase is about 0.1:1 to about 1:1; separating the washed aqueous raffinate and organic wash extract phases, and combining the organic wash extract phase with the extraction solvent of step (A) or with the organic extract phase of step (B).
 13. The process according to claim 12 wherein the wash solvent comprises propane, butane, hexane, heptane, decane, methylcyclohexane, methylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichloroethane, benzene, toluene, xylene, isoparaffinic mixed hydrocarbons having a boiling range between 90 and 325° C., or a combination thereof; and the wash modifier comprises n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, perfluorooctanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, bis(2-ethylhexyl)hydrogen phosphate, n-hexanol, 2-ethylhexanol, 2-ethylbutanol, n-octanol, isooctanol, n-decanol, isodecanol, or a combination thereof.
 14. A process for recovering an acid catalyst from aqueous glycolic acid, comprising (A) extracting an aqueous glycolic acid mixture, comprising (i) about 70 to about 90 weight percent glycolic acid, based on the total weight of the aqueous glycolic acid mixture, and (ii) about 1 to about 10 weight percent of an acid catalyst comprising sulfuric acid, methanesulfonic acid, methanedisulfonic acid, methanedisulfonic acid, bis(methylsulfonyl)methanesulfonic acid, trifluoromethanesulfonic acid, 1,1,2,2-tetrafluoroethanesulfonic acid, or a combination thereof; with an extraction solvent, comprising (i) about 5 to about 45 weight percent, based on the total weight of the extraction solvent, of a tertiary amine comprising tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trioctylamine, triisooctylamine, triisodecyl amine, tridodecylamine, tridecylamine, dioctyldecylamine, didecyloctylamine, or a combination thereof; (ii) about 5 to about 45 weight percent of a modifier comprising 2-ethylhexanoic acid, lauric acid, bis(2-ethylhexyl)hydrogen phosphate, perfluorooctanoic acid, or a combination thereof, wherein the weight ratio of the modifier to the tertiary amine is about 1:1 to about 5:1; and (iii) about 10 to about 90 weight percent of a diluent comprising hexane, heptane, decane, methylcyclohexane, benzene, toluene, xylene, isoparaffinic mixed hydrocarbons having a boiling range between 90 and 325° C., or a combination thereof; to form an aqueous raffinate phase comprising a major amount of the glycolic acid contained in the aqueous glycolic acid mixture and an organic extract phase comprising a major amount of the acid catalyst contained in the aqueous glycolic acid mixture; (B) separating the aqueous raffinate and organic extract phases; (C) extracting the organic extract phase from step (B) with an aqueous formaldehyde solution, comprising about 35 to about 85 weight percent formaldehyde, based on the total weight of the aqueous formaldehyde solution, to form an aqueous formaldehyde extract comprising a major amount of the acid catalyst contained in the organic extract phase from step (B) and an organic raffinate phase comprising a minor amount of the acid catalyst contained in the organic extract phase; (D) contacting the aqueous raffinate phase from step (B) with a wash solvent comprising about 80 to about 100 weight percent, based on the total weight of the wash solvent, of a wash diluent comprising hexane, heptane, decane, methylcyclohexane, benzene, toluene, xylene, isoparaffinic mixed hydrocarbons having a boiling range between 90 and 325° C., or a combination thereof; and about 0 to about 20 weight percent of a wash modifier comprising 2-ethylhexanoic acid, lauric acid, bis(2-ethylhexyl)hydrogen phosphate, 2-ethylhexanol, 2-ethylbutanol, n-hexanol, n-octanol, n-decanol, or a combination thereof, to form a washed aqueous raffinate phase and an organic wash extract phase, wherein the weight ratio of the wash solvent to the aqueous raffinate phase is about 0.1:1 to about 1:1; (E) separating the washed aqueous raffinate and organic wash extract phases; and (F) combining the organic wash extract phase with the extraction solvent of step (A) or with the organic extract phase of step (B).
 15. The process according to claim 14 wherein the aqueous glycolic acid mixture is prepared by process comprising carbonylation of formaldehyde in the presence of a sulfuric acid catalyst.
 16. The process according to claim 15 wherein the aqueous formaldehyde solution of step (C) comprises about 40 to about 55 weight percent formaldehyde and the aqueous formaldehyde extract of step (C) is passed to the glycolic acid process.
 17. The process according to claim 16 wherein the acid catalyst comprises sulfuric acid; the amine comprises tris(2-ethylhexyl)amine; the modifier comprises 2-ethylhexanoic acid; the diluent comprises hexane, heptane, decane, or a combination thereof; the wash solvent comprises hexane, heptane, decane, isoparaffinic mixed hydrocarbons having a boiling range between 90 and 325° C., or a combination thereof; the wash modifier comprises 2-ethylhexanoic acid, n-hexanol, n-decanol, or a combination thereof; and the weight ratio of the modifier to the tertiary amine is about 2:1 to about 4:1.
 18. The process according to claim 17 wherein the aqueous formaldehyde extract comprises about 0.5 to about 10 weight percent sulfuric acid, based on the total weight of the aqueous formaldehyde extract. 